This is John Stuart Mill on the basic principle of a free society found in his On Liberty:

“The object of this Essay is to assert one very simple principle, as entitled to govern absolutely the dealings of society with the individual in the way of compulsion and control, whether the means used be physical force in the form of legal penalties, or the moral coercion of public opinion. That principle is, that the sole end for which mankind are warranted, individually or collectively, in interfering with the liberty of action of any of their number, is self-protection. That the only purpose for which power can be rightfully exercised over any member of a civilised community, against his will, is to prevent harm to others.” [My bolding]

I have an article at Quadrant Online on The Right and Will to Defend Ourselves. What do I think of the state taking strong measures to protect us from the harm that others wish to do. I am all for it. There is no single simple overriding principle that is the final arbiter in what actions a state may take to protect me from the harm others wish to do. Here is Isaiah Berlin, whom I quote in the article, discussing the same thing:

If these ultimate human values by which we live are to be pursued, then compromises, trade-offs, arrangements have to be made if the worst is not to happen. So much liberty for so much equality, so much individual self-expression for so much security, so much justice for so much compassion.

My point is that some values clash: the ends pursued by human beings are all generated by our common nature, but their pursuit has to be to some degree controlled — liberty and the pursuit of happiness, I repeat, may not be fully compatible with each other, nor are liberty, equality, and fraternity.

Berlin not only understood Mill perfectly well, that would be where he would have found his own principle first stated. Minority opinion is one thing which must be protected to the ends of the earth; the call to murder one’s fellow citizens is quite another thing altogether.