Well, more than W, but most of the blame should go to the actual bastards doing the horrible acts.
That's like saying that Neville Chamberlain and the Allied countries that imposed the terrible Treaty of Versailles terms shouldn't be blamed at all for Nazi Germany and all of the blame only goes to Hitler and the Nazis. Well of course the Nazis alone are primarily responsible for their actions, that much is obvious. But that hardly exonerates the other mentioned people whose actions both led to their rise and were quite obviously foolhardy, even at the time.
No, that's like saying Ralph Nader is to blame for ISIS because without him, Bush would never even have been elected to begin with.
Neville Chamberlain was directly involved in Hitler's military success because his Treaty of Munich allowed more time to Hitler to build up the Wehrmacht and invade Poland (btw, you've already lost this debate based on Godwin's law). When Bush left office, no one was talking about ISIS. They were an irrelevant, powerless group. The group's rise has occurred in the past two years, and Syria was instrumental. If the democratic forces in Syria had triumphed and Assad been overthrown, there would never be the vacuum of power in western Syria that allowed such a radical group to thrive.