This isn't using a single mark to refer to a product for criticism and commentary; this is using an unlimited number of marks for promotion of the registrar's sites. (In addition to using the mark in the ways you mentioned.)
That is, the registrar's goal isn't to refer to PayPal, but to use the domain PayPal.sucks (and potentially every protected mark plus ".sucks") to draw traffic.
I guess the legality of this use will need to be decided by the courts.