For decades conservatives have accused liberal Supreme Court majorities of judicial activism, by which I mean sweeping aside democratically adopted laws and deeply rooted societal traditions to impose their own policy preferences based on highly debatable interpretations of the Constitution’s language and established meaning. On Thursday, the five more conservative justices — and in particular Chief Justice John Roberts and Samuel Alito, who went well beyond anything they’ve said before — forfeited whatever high ground they once held in the judicial activism debate.

I refer, of course, to the hugely important 5-4 decision freeing all corporations and, by clear implication, labor unions to spend unlimited sums supporting or opposing federal candidates.

The majority’s sweeping and unprecedented interpretation of corporations’ First Amendment rights, written by Justice Anthony Kennedy and joined by Antonin Scalia and Clarence Thomas, as well as Roberts and Alito, wiped out federal laws dating back 63 years and two major precedents.

And while the Court’s green light for "independent expenditures" of corporate funds on elections left intact the ban on direct corporate contributions to candidates, it nonetheless risked increasing the already worrisome dependence of candidates on various forms of big-business and big-labor support.

Kennedy all too cavalierly bats aside a compelling argument for banning executives from spending shareholder funds on elections.

This is not to join in liberal alarums that the decision in Citizens United v. Federal Election Commission will necessarily swamp federal elections under a deluge of corporate money. Nobody really knows how big a difference it will make. Corporate freedom to spend on elections does not seem to have had much impact in the 26 states that already allow it, perhaps because big businesses are wary of making enemies as well as friends. And union spending for Democrats will offset any Republican advantage in corporate spending.

Nor do I put stock in the four liberal dissenters’ suggestions that they are any more committed to "judicial restraint" or respect for precedent as a neutral principle than are their conservative colleagues.

While the conservatives’ view of free speech rights in this area seems too broad, the liberals’ view — especially by comparison with their capacious protection of, say, pornography and nude dancing as free speech — seems too narrow.

All nine justices passed up an opportunity to carve out a pragmatic, principled exception to Congress’s overbroad 63-year-old ban on corporate spending on federal elections, an exception that could have amply protected Americans’ free speech rights without allowing big business executives to use other people’s money — that of shareholders — to buy politicians.

Specifically, the Court should have upheld the ban on election spending of shareholder funds by business corporations but allowed election spending by nonprofit ideological groups, such as the Sierra Club, the National Rifle Association, and the ACLU, whose members give them money precisely for the purpose of influencing governmental policies.

Kennedy’s majority opinion is utterly unconvincing in arguing that unleashing big business corporations to spend shareholder funds to support and oppose candidates is necessary to protect the rights of those shareholders and executives who wish to aggregate their money for such purposes.

As the dissenters point out, all corporations are free to create political action committees that can spend on elections as much money as they can collect from officers, shareholders, and others who choose to donate for that purpose. Corporations are also free to spend stockholder funds without limit on "issue ads" and on lobbying.

It’s true, as Kennedy writes, that the administrative burdens involved in forming a PAC are considerable. But these burdens are not a serious problem for big, or even not-so-big, businesses. And while they are a problem for the vast majority of corporations owned by one or a few people, such people can easily spend as much as they choose on elections individually.

Kennedy also stresses that the main arguments adopted by the now-overruled precedents for banning corporate spending of shareholder funds on elections — that such spending involves "corruption" or "the corrosive and distorting effects of immense aggregations of wealth that are accumulated with the help of the corporate form" — are unconvincing or problematic.

He’s right about that. But Kennedy all too cavalierly bats aside a far more compelling argument for banning corporate executives from spending shareholder funds on elections.

The money does not belong to the executives who decide how to spend it; corporate law allows them to spend it only to serve their companies’ parochial economic interests; and the vast majority of the individual shareholders to whom the money does belong have not chosen to spend it on elections and would in many cases disagree with the executives’ candidate preferences.

Kennedy and Chief Justice Roberts in a concurrence belittle this so-called "shareholder protection rationale" for banning corporate election spending.

But even apart from protecting the interests of shareholders who might object to having their money spent to advance politicians they don’t support, big-business spending on elections distorts the political process by injecting large sums of individuals’ money in support of candidates whom they have not chosen to support — regardless of whether those individuals are motivated to object or even care.

Most people own stock through mutual funds and retirement plans and don’t pay attention to election spending by individual companies of which they own tiny percentages. Why should a corporate executive or anyone else be allowed to pour other people’s money into political campaigns as though the shareholders wanted that done?

In this regard, the dissenters were quite right to suggest that in the majority’s distended view of corporate First Amendment rights, "multinational corporations controlled by foreigners" — who have no right to spend individually on elections — could spend unlimited sums on federal elections. The majority backhandedly acknowledged that this might be troublesome and then moved on.

Advocates of unleashing all corporations point out that the current ban sits somewhat awkwardly alongside the congressionally conferred (and, I think, constitutionally mandated) license enjoyed by huge media corporations — including Disney’s ABC — to spend whatever they please on election advocacy.

This is perhaps the majority’s strongest point. But it overlooks key distinctions: People who buy stock in media corporations are on notice that one of their primary goals is to spend money on federal elections, including editorials for and against candidates. In addition, the First Amendment protects the freedom "of the press" as well as the freedom of speech, and thus suggests that the Framers expected the media to enjoy some protections that others might not enjoy.

Apart from media corporations, the one significant group of corporations that aggregate the money of individuals who want their money spent on elections, but that are in many cases so small that forming PACs would be burdensome, are nonprofit ideological corporations.

And this points to the one serious First Amendment defect in the campaign finance rules that the justices have now struck down. In adopting the 2002 McCain-Feingold law, Congress added to its justifiable ban on "electioneering" broadcast ads by business corporations an utterly unjustified amendment by the late Sen. Paul Wellstone, D-Minn., extending the ban to nonprofit ideological corporations formed by people who want to pool their funds to promote their political views.

(The 1947 Taft-Hartley Act imposed a narrower ban on corporate "express advocacy" for or against candidates.)

Congressional supporters made clear that the purpose of the Wellstone amendment was not to fight corruption but rather to stifle "negative attack ads" criticizing themselves and other incumbents (as well as challengers).

The justices should have struck it down while leaving intact the ban on electioneering by business corporations. But not one of the nine proposed to do that.

While the conservative majority thus gave undue First Amendment protection to business executives to electioneer with shareholder funds, the liberal dissenters would have sacrificed the First Amendment rights of individuals to aggregate their money and spend through nonprofit ideological corporations.

Moreover, the liberals’ suggestions that Congress can and should curb the spending of great wealth amassed in the business marketplace on elections could be extended to justify curbs on wealthy individuals’ spending.

Such a step might be understandable in extreme cases. But it would be limitless in its potential for multiplying wealth-based restrictions on speech. It would also wipe out a cardinal principle of the campaign finance precedents for which the liberals affect such respect: that "government may [not] restrict the speech of some elements of our society in order to enhance the relative voice of others."

The liberals argue that business spending on campaigns, including independent expenditures, creates the kind of appearance of indebtedness and of corrupt dealings that justify banning large (above $2,400) contributions from individuals and all corporate contributions.

But independent election spending by business corporations is no more corrupting than the independent spending of vast sums by super-rich individuals such as George Soros, which the First Amendment properly protects.

In any event, while the liberal justices might like to tack too far away from vigorous First Amendment protection of political speech, the conservatives are on top for the foreseeable future.

I wrote in a September 19 column that "it would look a lot like judicial activism for the more conservative justices to ram through, for no good reason, a 5-4 decision smashing a cornerstone of campaign finance law; overruling precedents that date to 2003 and 1990; and brushing aside congressional concerns about corruption and its appearance — all in a case that does not even involve a business corporation."

Now they’ve done it.