There is a difference between 'not funny' and 'I don't find it funny' - and that's an important distinction to make because, whilst there might be subject matter you find distasteful and disgusting, that doesn't mean it isn't funny. Comedy is about subversion - Carlin isn't joking about rape, he's explaining how and why rape isn't exempt from the rules of comedy. We need to be careful about the distinction between whether something is a joke or not independently of whether we find it funny - we blur those lines at our cost. There are places in the world where comedians don't exist and they're very much a product of a liberal democratic state.

And if you don't like Carlin's take on it, then you might appreciate Truscott's. https://www.theguardian.com/culture/2014/may/14/adrienne-truscott-asking-for-it-review-comedy

She's effectively reappropriating the rape joke, she performs without anything on below the waist... and makes the rape joke a feminist tool. Carlin and Truscott are doing different things with the rape joke - they're doing clever things and that's really what comedy is about. You don't have to like what they do, but comedy isn't about what you as an individual find funny, it's about how expectation is subverted in a way that some people find funny.