Why stop totally justified sanctions on an evil butcher who is at war with Israel and is backing Hezbollah financially and materially, and is right now fighting the people who help the US fight ISIL?
Because it is not in America's interest.
What
was in America's interest was the status quo where Assad stayed in his Syrian & Lebanese sandbox and kept a lid on things in Syria. Which he likely would have managed by now if we had stayed the heck out of the Syrian mess. ISIS would be a footnote in history, one of several rebel groups crushed by Assad, rather than a disruptive force in the ME that threatened ME oil production. Oil which the US sees very little of and is even less significant due to the fracking oil boom in the USA.
If Israel has problems with Hezbollah and Assad, Israel is capable of dealing with them. If Israel is offended that Assad treats his people poorly, let Israel give them aid.
The majority of people in the world are ruled by evil butchers. It is not America's responsibility to liberate their victims. That has been tried over & over and found to be a fool's errand.
The trouble with the Middle East is that it's full of Middle Easterners
Basically.
So some of you are saying we should wait until we have another 9/11 type event on our soil before we act?
We ought not deploy against every group that hollers they hate America before they even have the capability of pulling off a 9/11. We'd end up turning the ME and much of Asia & Africa into depopulated wilderness.
Some groups, like Somali and Nigerian pirates,
do rate killing out of hand before they can hit the USA due to their disruptive effect on commerce. But you will recall that we did NOTHING to the bases/villages these pirates operate out of. So, on the one hand we deploy against and bomb a group incapable of hitting the USA and that could be managed by locals, but we sit back and refuse to destroy the bases of pirates disrupting commerce that does effect us.
FTR, were we to experience a 9/11 magnitude attack every 20 years, that would average out to 200 people/year. That is less than half as many folk who are murdered in Chicago every year.