As others have mentioned, people use other metaphors like "killed", "murdered", or describing something as a "cancer" all of which are very common. However, the word "rape" might be worthy of being an exception because where you might see the other words being used by legitimate news sources, eg "match fixing is a cancer infecting the sport", you'd never hear the word rape really being used. Not all words are treated equally in our culture - and I don't think it's useful to pretend that are, so the fact that we allow the word "killed" is not a valid excuse to allow the word "rape".
Using the word "gay" in a derogatory way is another one, which is clear cut IMO because, as others have pointed out, while the other terms are negative in their nature and are used to describe negative things, it's not a coincidence that "gay" was chosen to mean "bad" instead of "straight" or something like that.
So I think the policy is pretty fair.