There are no alternatives. The US showed erdogan the door a dozen times and everytime he crawls back. And not only him but Akar too. This will end in the invasion of nothern syria after our soldiers get attacked and killed with the weapons the US delivered and everybody will say "why did we not invade them sooner?". Preemptives strikes are how you deal with threats, you don't wait until they get free Abrams and Howitzer to attack your soldiers. You crush them.
It is not like we didn't give them a alternative plan that is just as good if not even better but they say no everytime. The US doesn't care about Raqqa or ISIS it cares about its plans for the future and the only proxy they will be able to use for it is the ypg as they sell themselves to everybody. Who have they left? The arabs hate them be it assadists or rebel, turkmens hate them. Kurds, better said pkk, are the only ones left for them to play with. PKK is the only way for them to stay revelant in the ME, as all other proxies have been betrayed by them. And if Turkey crushed them under its boot they have nothing in the ME to control and have influence over.