We collect feedback from YC founders on investors (we have a giant database of this). If you mistreat founders, we don't invite you to Demo Day. This isn't permanent--if you stop mistreating founders we start inviting you again. Also, it's possible that our founders are wrong in their assessment of how a particular investor is treating them, but investors have enough advantages in the system and we unashamedly take the side of our founders.
EDIT: I also never think these things are black and white, and that all of us have good and bad parts. I've heard from plenty of founders that Jason has been very helpful to their companies.