THERE IS only one acceptable response to Thursday’s violent outburst outside a San Jose Donald Trump rally: unreserved condemnation. Anti-Trump demonstrators chased peaceful Trump supporters, threw eggs, jumped on cars and even hit people leaving the campaign event. John Podesta, Hillary Clinton’s campaign chairman, quickly and rightly repudiated the episode, tweeting, “Violence against supporters of any candidate has no place in this election.” Unfortunately, others had trouble leaving it at that.

The violence was not, as some left-leaning politicians and commentators have argued, contextualized and therefore somewhat justified by Mr. Trump’s near-constant racial provocations. Nor was it the reflection of some new illiberalism on the left, as some right-leaning observers have claimed. They pointed the finger at out-of-control PC culture — as if there were no such thing as political riots before the invention of trigger warnings.

No, this was nothing more than run-of-the-mill thuggery. Journalists on the ground reported that some of it may have been the work of gang members or self-proclaimed anarchists. Some of it was undoubtedly perpetrated by people who were simply very angry at Mr. Trump but who, unlike nearly all Americans disgusted with the presumptive GOP nominee, were unable to control themselves.

Even some of those who criticized the protesters got the ethics of the situation wrong, stressing that anti-Trump violence is politically counterproductive. To be sure, the protesters diverted attention from the awful things Mr. Trump himself has said over the past several days. The candidate will now accuse his opponents of intimidation for the rest of the election season, ginning up support among those sympathetic to his message and encouraging a violent backlash against the protesters.

However, these arguments miss a more fundamental point: In a free society, political violence is inherently wrong.

Even if you think Mr. Trump is a threat, the United States is not Nazi Germany. It is a country with a functioning liberal order guaranteeing basic civil protections. It is a democracy with institutions that check the power of each branch of government and allow for extreme differences in political views to be expressed through an orderly, representative process that demands compromise. In this context, argument, activism and organization are the legitimate tools of political action. Violence is not and cannot be.