It's not racist because Islam is a belief system. I'm Muslim and i really don't care if people criticize Islam. What I have an issue with is people criticizing Muslims.
There is 1.6 billion of us. We aren't all the same and don't have the same ideologies. Just like you find different denominations of Christians ranging from your bat shit crazy westbro church members to your more liberal and progressive Christians who are about love and peace. You'll find the same with Muslims.
the westbro church churchies haven't knocked over any sky scrapers, blown up subways, ran over scores of people in trucks, done genital mutilation, massacred neighbors and co workers that gave them parties in honor of their new born babes, drowned people in cages, cut off heads of those who disagreed with them, massacred journalists and artist who made jokes about them, raped women who don't cover up properly. etc.