The other side of that is that those who would have had us not go to war would have had us leave Iraq and Afghanistan in the hands of Saddam and the Taliban. That seems reason enough, and if anything was left far too late. How it is handled and what happens afterwards is another matter, and given what happened with Iraq (and the successes there, particularly for the rights of the people, must not be forgotten) means that it is unlikely that establishing a free democracy in a land of brutal despotism will ever be tried again. We may yet have cause to regret that attitude in the decades to come.
Isolationism, on the other hand, is practically impossible, but morally and legally impossible for us as well. We are signatories of the
Convention on the Prevention and Punishment of the Crime of Genocide, and are required by international law and human decency to intervene in the event of genocide, ie mass race murder, and to punish those responsible. Which makes it all the more reprehensible that we didn't lift a finger for Rwanda and had to be persuaded by internal activists to intervene in Kosovo after watching it take place for some time. Bear in mind that if that had been permitted to continue we would have seen, in a land an hour's flight from Berlin, two from London, the rise of exactly the kind of fascism and horror eliminated from Europe in 1945.