Obama has never been anti-war. In his famous 2002 speech he said he was not anti-war, he was ant--stupid war. By definition, any war he would engage in he wouldn't think was stupid.
The entire anti-war left is anything but antiwar or anti-violence (the left never is) but they do have a problem seeing any sort of violence perpetrated against anyone who meets the standards of being anti-American, not American like, is bad, guilty of anything heinous, evil, anybody with any sort of pigment to their skin, etc.