Although pure criticism is not exactly what they would like people to post there, feedback forum is probably the best place to look for it.
But are they arbitrarily removing (at least) some of it?
It is very rare that such criticism is quoted in the news, but here is an example:
Wrote one user: "Craig tried to act all innocent about prostitution on CL, but he created a whole category for it: Erotic Services! Duh!"
Another agreed: "You caught how C. Newmark was acting coy about the problem. I saw that, too, and it was very disappointing."
I tried to find the quotes above (searched the feedback forum) and they didn't seem to be there... also looked in the "Isle of Misfits" (where questionable threads/posts end up) ... nothing!
P.S. If I somehow missed them and you know they are there... please let me know! (I really wanted to see the whole discussion). Thanks! D.