He's being contradictory about the idea that ONLY SITH DEAL IN ABSOLUTES. Obi-Wan Kenobi is a Jedi, not a Sith, and he apparently deals in absolutes too. I cannot make this any more clear.
Well, actually, if you are saying that Obi-Wan's statement doesn't stand for his personal opinion but for the jedis in general then you are dealing in absolutes. This makes you a sith then. QED.