That people on the political left have a certain set of opinions, just as people do in other parts of the ideological spectrum, is not surprising. What is surprising, however, is how often the opinions of those on the left are accompanied by hostility and even hatred.

Particular issues can arouse passions here and there for anyone with any political views. But, for many on the left, indignation is not a sometime thing. It is a way of life.

How often have you seen conservatives or libertarians take to the streets, shouting angry slogans? How often have conservative students on campus shouted down a visiting speaker or rioted to prevent the visitor from speaking at all?

The source of the anger of liberals, “progressives” or radicals is by no means readily apparent. The targets of their anger have included people who are non-confrontational or even genial, such as Ronald Reagan and George W. Bush.

It is hard to think of a time when Karl Rove or Dick Cheney has even raised his voice but they are hated like the devil incarnate.

There doesn’t even have to be any identifiable individual to arouse the ire of the left. “Tax cuts for the rich” is more than a political slogan. It is incitement to anger.

All sorts of people can have all sorts of beliefs about what tax rates are best from various points of view. But how can people work themselves into a lather over the fact that some taxpayers are able to keep more of the money they earned, instead of turning it over to politicians to dispense in ways calculated to get themselves re-elected?

The angry left has no time to spend even considering the argument that what they call “tax cuts for the rich” are in fact tax cuts for the economy.

Nor is the idea new that tax cuts can sometimes spur economic growth, resulting in more jobs for workers and higher earnings for business, leading to more tax revenue for the government.

A highly regarded economist once observed that “taxation may be so high as to defeat its object,” so that sometimes “a reduction of taxation will run a better chance, than an increase, of balancing the Budget.”

Who said that? Milton Friedman? Arthur Laffer? No. It was said in 1933 by John Maynard Keynes, a liberal icon.

Lower tax rates have led to higher tax revenues many times, both before and since Keynes’ statement — the Kennedy tax cuts in the 1960s, the Reagan tax cuts in the 1980s, and the recent Bush tax cuts that have led to record high tax revenues this April.

Budget deficits have often resulted from runaway spending but seldom from reduced tax rates.

Those on the other side may have different arguments. However, the question here is not why the left has different arguments, but why there is such anger.

Often it is an exercise in futility even to seek to find a principle behind the anger. For example, the left’s obsession with the high incomes of corporate executives never seems to extend to equally high — or higher — incomes of professional athletes, entertainers, or best-selling authors like Danielle Steel.

If the reason for the anger is a feeling that corporate CEOs are overpaid for their contributions, then there should be even more anger at people who get even more money for doing absolutely nothing, because they have inherited fortunes.

Yet how often has the left gotten worked up into high dudgeon over those who inherited the Rockefeller, Roosevelt or Kennedy fortunes? Even spoiled heirs like Paris Hilton don’t really seem to set them off.

If it is hard to find a principle behind what angers the left, it is not equally hard to find an attitude.

Their greatest anger seems to be directed at people and things that thwart or undermine the social vision of the left, the political melodrama starring the left as saviors of the poor, the environment, and other busybody tasks that they have taken on.

It seems to be the threat to their egos that they hate. And nothing is more of a threat to their desire to run other people’s lives than the free market and its defenders.