Syria borders Israel, our only true friend in the region, and you see no essential interest?
Russia has never threatened Israel.
And Assad was being overtly non-aggressive.
What would Israel be faced with if ISIS ran Damascus and had Assads weapons?
Assad is less of a risk to Israel than ISIS. He's a somewhat rational actor.
With that out of the way, the West needs to realize - as we remember 911 - that militant Islam is a major threat across the globe. Whether it is Boko Haram and Al Shabaab in Africa, or Abu Sayyaf in the Philippines, or any of the various 'scion of Al Qaeda' that have sprung up around the ME, the fact is that ISIS is the most cogently effective Jihadi group to emerge. They did something that Osama never thought possible ...have an actual fledgling caliphate, hold land, take taxes, and have sustained success. They are consolidating power in Iraq, Syria, and parts of North Africa. In West Africa Boko Haram has pledged allegiance. Other groups may soon follow.
Basically, you are looking at GlobalJihad.org
Now, the West's process of regime change - be it removing Saddam, or removing Qaddafi, or removing Assad - has been shown to be unworkable. We almost lost Egypt as well. Removing 'bad men' without having a viable alternative is foolish. Simple!
Thus, if Assad and Russia smiting ISIS is unpalatable, then the only thing is for the West to do something about it. Smite ISIS. Drive them to their doom and smash them so hard that the genetic memory of Jihadi is imprinted with what happens when the West decides to act.
Unfortunately, it appears that the West is not willing to do much. At least so far. Which reminds me of the story of the good Samaritan (there's a reason he is called a GOOD Samaritan). Before he came along and helped the injured man, two men who were 'holy' passed him without offering aid. Only the GOOD Samaritan decided to do anything.
While Russia is not 'nice' and Assad is a veritable monster, the thing is if the West will not do squat then it better not complain when others fill that void (for good or ill, as countries always have their own interests and I'm sure Russia is not doing it for CSR or goodwill). If the West will not step up, then it really shouldn't be screaming and shouting.
It would be like the two holy men chastising the good Samaritan for assisting the injured man they themselves had just walked past.
What's ironic is this ...someday the West will rue that it never squashed ISIS back when it would have been simple to do so. A saying from my native land is that 'the best time to kill a crocodile is when it is in its egg.'
However, it appears the West prefers fighting off 18 foot scaled leviathans rather than smashing soft crackly teeny weeny eggs!!!!