"If liberty means anything at all it means the right to tell people what they do not want to hear." - George Orwell
Science offends the politically correct because science lends itself to objective evidence and objective truth. Political correctness, however, lends itself to subjective perception, feelings, and the false claim that all cultures, religions, and political systems are equally good (with the possible exception of those that have been shown to work).
By making it a thought crime to say anything that may offend somebody, somewhere, at some unspecified time in the past, present, or future, they are making it a potential thought crime to say anything. Which is the most effective way to shut everybody's mouth.