You could have looked that up yourself. I'm going to assume you haven't read this before.
Of course you can continue to believe it was because of WMD's and Halliburton if you want.
Destroying the "great evil" that was Saddam landed us with ISIS, going off half cocked with ISIS will create what. There will be no "and the great Satan was destroyed. The end." because people will still be living after you declare victory and a power vaccum will exist. A long term solution is not to meet them with force, but to weaken their powerbase. However this is hard and requires forethought and planning where as dropping bombs makes it look like you're Doing Something(TM) now. Screw what might happen in the future.
No, leaving Iraq prematurely is what fueled ISIS. A long term solution would have been to do exactly what we did in Germany, Korea, and Japan. There's a lot of things I'd like to say in response to your other points, but frankly I don't have the time or will to do it on Slashdot. I just don't care that much.