I’ve thought about this kind of thing a lot, but if you look into the history of LSD use you quickly find yourself at a dead end.
Some of the first people to heavily experiment with LSD were CIA agents. Before and during the MKULTRA experiments, agents consumed large doses of the psychedelic, occasionally under very strange circumstances (for a large intelligence agency). However, these same agents continued in their duties to the state. They spied, tortured, and likely killed, even after having intense psychedelic experiences.
The point being, psychedelics do not transform you into a peace loving hippie-type simply by virtue of their use. They create the conditions for change, but they don’t provide it, and they don’t always provide it in the same direction, i.e. in the direction the 60s counter-culture moved.
That counter-culture became what it was because of already underlying ideas and ideals. LSD enhanced these, it did not create them. In the same way, giving an ISIS member LSD will not turn them into what you would like. It could allow them to be open to a new way of thinking and perceiving, but you’d have to create the circumstances around them to move them in the positive direction you speak of.
And that is the big challenge.
So really there’s no simple way around it.
Additionally, the idea of spraying a population centre with a fine mist of a psychedelic substance was debunked a long time ago. The CIA and others tried it in a controlled fashion — read as, at parties held by US citizens unbeknownst to them. It didn’t work. LSD is too delicate and it doesn’t disperse as you’d perhaps like.
You also can’t put it in a water supply, unless you manage to completely purify that water supply first.