"Genuine question about free speech as I find the concept confusing. At what point does free speech become hate speech? Where is the line drawn between just airing vulgar views and actually being considered dangerous under law?"
Inciting violence, e.g. 'I don't like group X for reason A' vs 'The sooner we start killing Group X the better'.
"I struggle with the whole 'their country, their rules' thing. While I certainly agree we had no right to get involved in Vietnam, I think we had no right to leave Rwanda to struggle alone IYSWIM?"
Humanitarian aid for countries suffering from 'an act of God' is one thing, assuming it'll be used appropriately. Meddling with people who create their own disasters, unless that disaster threatens you in some way, is a different matter. I wouldn't send my child to die in someone else's country just because they've decided to defecate in it.