[Yamer]

I think Werner felt that he could get away with it because of how close he thought he was to Mike. As he said, he thought he would come back and "his friend Michael" would be upset, but understand and forgive him. In fact, I believe this is the major turning point in Mike's character in becoming the cold, calculated cleaner we see in BB.

The only characters we see Mike care about in BB are Kaley and Jesse, and I think it's clear that it's because he sees his son in Jesse (a mostly wholesome victim). Mike has been softer in BCS, and him letting his guard down with Werner and the group and then having to put him down because he was too soft on him is going to be transformative.