I believe everyone has the right to self-defense whether American, Arab, or whoever.
The issue here is America instigated the problem, and now everyones coming to the conclusion "now we have to get rid of them!", theres no such thing as getting rid of IS without a huge amount of collateral damage (which will just create a new IS later down the road from blowback).
Not to sound like an advocate of IS, but the man who murdered Foley said the life of the next American rests on the decision of Obama, meaning if you attack us again, we'll kill more Americans. But the stubbornness and bravado of Americans cannot accept that, and they will at the risk of their own people, will try to "punish IS". Clearly if given the option, IS will choose not to engage the US in a fight, so if the US halts military operations IS is likely to go back to fighting within the Iraqi and Syrian borders.