The US has assisted in efforts to destabilize both Iraq and Syria, including assistance for Islamists. That is not controversial. Whether the US at any time assisted ISIS or AQ is uncertain, but it is known that there have been concessions (see WikiLeaks cables on Syria), and it is likely that the early parts of these campaigns were abetting these groups specifically. It is certainly true that "shifting alliances" have meant that US support has easily gone to al Nusra and ISIS indirectly. The Sunni in the provinces controlled by ISIS have been under attack by their central governments, crucially when their militias were outlawed in Iraq. So aid given is somewhat fluid in where it ends up. The US still has a responsibility to insure that aid does not end up in the hands of terrorists.
Nonetheless, the explicit criminality of US intervention is known, too. Gaddhafi represents a dramatic example - the US literally paved the way for his captors, without any attempt to detain him for ICC trial. This was an affront to international law which the US made no attempt to hide. It deprived the world of important information, and a resolution to Gaddhafi's crimes, for victims and watchdogs.
I am not in Libya, Russia or Syria. The democratic deficits of US enemies are apparent (as are those of US allies). I am in the US - which is responsible for its influence and military presence, and which uses my name and others' to commit war crimes. That is quite a contradiction to our democratic principles. I don't think most US citizens would like to officially support war crimes, targeting of civilians and civilian infrastructure. I realize that it is easy, and not quite accurate, to give the US full agency when it comes to the worst outcomes it helps to produce. But that does not change its crimes, nor the responsibility thereof, and our responsibility, to stop such crimes done in our names.
International Convention for the Suppression of the Financing of Terrorism:
1. Any person commits an offence within the meaning of this Convention if that person by any means, directly or indirectly, unlawfully and wilfully, provides or collects funds with the intention that they should be used or in the knowledge that they are to be used, in full or in part, in order to carry out:(a) An act which constitutes an offence within the scope of and as defined in one of the treaties listed in the annex; or
(b) Any other act intended to cause death or serious bodily injury to a civilian, or to any other person not taking an active part in the hostilities in a situation of armed conflict, when the purpose of such act, by its nature or context, is to intimidate a population, or to compel a government or an international organization to do or to abstain from doing any act.
Lets put this to rest. The usage of terror, directly or indirectly, and the treatment of human life as a fungible, consumable asset is illegal, immoral, undemocratic and illegitimate - whether in the form of Shock and Awe, Protective Edge or extrajudicial killings by drone strikes.
United Nations - International Convention for the Suppression of the Financing of Terrorism