If only the Sith deal in absolutes, why does Obi-Wan say it that way?

The Jedi are hypocrites. The major theme of the prequels was that the Jedi had grown corrupt and abandoned the Living Force for orthodoxy and bureaucracy, and this was what caused them to be blind to the Sith, and to their own blindness.

Unfortunately the prequels were hamfisted garbage only suitable for selling toys to children and any semblance of political depth and nuance in the plot got tossed aside to make more room for the bumblefuck racist rabbit lizard that nearly destroyed the franchise.

He doesn't reject the light side in Anakin. He still accepts the dual, even as he sees his mentee going darker & darker side. He isn't dealing in absolutes. He is highlighting an extreme end.

Thank you one of thr replies (#2) for this general idea.

It did definitely but me for a long time. But this is a intolerance of fascism situation, intolerance of intolerance, which is the only thing tolerance cannot survive, must resist.

because the jedi aren't the good guys