What ItsAll is getting at, is that ISIS aren't a centrally organised group, but more of a franchise, with clusters of groups operating under the same banner. The France attacks probably weren't organised, funded, or equipped from Iraq or Syria, but from ISIS groups in Europe.
That's why attacking ISIS in Syria does little to make anyone in Europe safer.
There is also the issue of atrocities like France being carried out in order to provoke a reaction, it's the cycle of terror: anti-state action, provoking state reaction.
The more merciless the Western response, particularly if it creates a significant civilian "collateral damage", the more ISIS will be able to paint the West as the enemy to those living under ISIS rule and shoring up their support.
In short, bombing ISIS out of existence won't work, but will instead aid their recruitment.
That doesn't mean I think ISIS should not be fought, they should, but I think it needs a more nuanced approach then carpet-bombing vast areas.
Also, France's response mirrors that of Jordan, when the Jordian pilot was executed, Jordan immediately launched air-strikes and executed ISIS prisoners. Did that do much to counter ISIS, no, not really.