What could a western country do to effectively "combat the Wahabist ideology" of Saudi Arabia? Is it possible to win the hearts and minds of the Saudi's? Is this the choice - fight ISIL or fight some ideology?
Even if it could be done, and I don't think it really can over the long run, it is not a choice taken instead of attacking ISIL in Syria, Iraq and elsewhere, but in addition to it. They wantonly kill civilians, practically without regard to their religious beliefs, - they are thugs, bullies, enemies of justice and freedom wherever it is found. They should be destroyed if possible, but fought even if they can't. It is simple self-defense - whether their atrocities are carried out in Paris, Lebanon, Syria, Iraq or anywhere else.
May the good guys win.