Despite it often being claimed that Rorschach's moral world is seen only in terms of Black and White (His mask being the manifestation of this), it cold actually be observed that he only operates in relative Grays. Remember also, those black and white areas are constantly shifting their boundaries, in endless flux.
For what is a fundamentally psychotic character, the idea that the world can only be gauged on such an extreme spectrum is actually a type of cover, a way for Rorschach to enable his own behavior through a supposed ethical structure (however warped such a structure may be).
As Jersey pointed out,
Remember that Rorschach walked the streets of New York where hookers and whores were 'displaying their wares' and did nothing. Perhaps, in his mind, neither is a crime or [...]
The man isn't exactly a law dispenser; he is relatively literate of the law, but not to the extent of a professional enforcer, nor does he seem to be litigious himself. So, as you've noted yourself, his 'good-bad' spectrum is something entirely subjective, and is defined by his own code of behavior: which is both autonomous of and distinctly separate to the norms of society.
Given his mother's occupation, his total disenfranchisement, his penchant for masculine violence (if such a thing is so readily accepted) and his psychosis itself, is it any wonder he holds such little regard for a 'Bloated whore'.
Rorschach, as a Darkened Mirror to Dr Manhattan, seems to perceive and organize his experiences of reality in a lateral, dispassionate way. The violation of a human body is, as he himself notes, a 'moral lapse', but considering the Hallowed nature of The Comedians many achievement (not to mention a certain amount of sympathy for his philosophy) would perhaps allow him to dismiss the incident as trivial.
