at which point the other Muslims sects will go to war with them and happily fall into a long drawn out civil war.
heck we'll even make a fair bit of money selling arms to both sides
Both of you are assuming this won't have any repercussions at home. If IS "wins", they could well turn their attention to stirring up trouble here, in the US, everywhere.
And of course we'll have all those lovely jihadists returning "home" with their triumphant cries, preaching in UK mosques, calling on muslims to fight against the west and expand islam across the whole world.
Basically, they'll be emboldened, they'll have no problems recruiting, and their next targets will probably be closer to home.
