John Oliver also might be a rapist, or maybe a murderer, or both. The allegations against Cosby didn't come out until much later in his career, compared to Oliver today. Also, even if he hasn't raped anyone yet, that doesn't mean he doesn't want to and that he won't do it in the future, which would retroactively make him a rapist -- once you've committed a rape, it applies to everything you've done in the past and everything you'll do in the future.

What I'm saying is, if you want to discount everything Cosby has done based on a rape allegation, you ought to keep in mind, that the potential for it exists for Oliver too. The only conclusion that springs to mind, if you discount the possibility of Oliver being a rapist, is that you're subconsciously racist. Even if you're unaware of it, you're thinking something like "Oliver is a nice white man, so he'll never rape anyone, but that nigger definitely drugged and raped those women".