I'll wait to see the whole interview in context before I jump to any conclusions.
I don't know what exactly Denzel meant by the ex-slave comment but I don't think he is one of those hollywood leftwing nutjobs because of the following:
1) He didn't see the movie F-11. If he were a lefty he would want to support it and be there the day it opens.
2) During Michael Moore's Oscar speech and tirade against President Bush, the camera was on Denzel and he didn't look too pleased nor did he applaud.
3) Denzel has done plenty of pro-military movies (Antionne Fisher, Crimson Tide, The movie with Meg Ryan)
Denzel may have meant that war freed the slaves and now I am an ex-slave because sometimes war is necessary. At least that's what I hope he meant.