with the OP, i also know an anarchist who doesn't reject guilt as a motivation, but i can only think of reasons why guilt is a bad motivator.
primarily because it keeps people wrapped up in a monologue that is self-referential, but also because it can never be resolved. guilt is never really assuaged, it is a way of being in the world based on questions of worth. maybe more to the point, in my experience it makes people reactive and shallow.
sleeper, do you have examples of when it would be, or has been, good?