It's not about justifying "leaving him in his position". It is about what comes after Assad is driven out.
Believe it or not, it could be worse. Just look at some of the people fighting what's left of Syrian government armed forces. ISIS, for one. Much of the rest would fold like cheap suits to be rolled up in Persian rugs, resulting in Iranian influence becoming even more solidified.
Or what? Would they have Saudi benefactors (plus some fro Qatar, possibly Oman and the UAE)? The Russians would still be trying to get their fingers in the works. It could drive them to make further 'more' nice with Turkey (even though, in the deepest recesses of their minds, the Russians are dying for a chance to take Istanbul Constantinople).
Volatile situation(s) all around. Jared Kushner is a bit out of his league, I'd say.
Our wolfish "let's fight" Generals know how to fight. That's their job. They'd just as soon do what they know how to do, rather than sit around twiddling their thumbs. That can be a good thing, and it can be bad thing. Taking advice directly from Generals -- instead of asking them -- "what if?" and "could it be done>" can be approach tangled up, politically difficult challenges ---backwards.
He that chooses to live by gunboat diplomacy can die a hundred different ways, in the long run. His own people can be made to pay the price, too (and that's after his own troops pay with their lives, and having made others pay-pay-pay, too).
Whoever assumes power in Syria -- from U.S. perspectives -- better have some measure of approval of Israelis, and Saudis? I'm not the first one to take notice of that seemingly odd paring.
Also, lest we forget -- do not ever forget, the Iranians are anything but stupid. They may be a bit crazy, BUT they can read the tea leaves (and opium poppies, and non-state terrorists actors --some who have their support) as good or better than anyone in the Middle East.
The Kurds will still want a piece of Syria. And part of Northern Iraq. The Turks know the Kurds would want a big piece of Turkey. Erdogan would screw over his own mother with a splintery broomstick before he'd allow that to happen. Kurd's won't get any of the small part of Iran they desire, not without becoming Iranian puppet to far more extent than whatever they would be granted limited administration over present day slivers of far-Northwestern Iran -- that is, if the Iranians gave Kurds anything. Yet there they are, kind-of right in the middle of everything (that is not Israel).
Partition of Iraq too? Split off the Western Provinces, those ending up aligned with House of Saud and the Hashemites? (The better to keep the rug merchants at bay) Is that part of the plan? How long would that last? It all sounds like dirty pool, to me. Thank God I'm not a Kurd, or was born a Christian in Northern Iraq, or Syria. I'm sure I couldn't figure it all out, other than laying low, or fighting whatever was in front of of my nose, by turns. But who the hell could? It's a mass of confusion, deceit and (MORE than three-sided) bloody war.
Here are several satellite photos of the airbase.