Humiliation doesn't necessarily have anything to do with embarrassment. It can provoke powerful sexual emotions without actually having to be embarrassing.

For instance, one submissive I know fairly well from these forums likes being told what a dirty whore, or what a juicy cunt she is. She doesn't find the words embarrassing at all, but she does find them to be a powerful turn-on when I say them to her.

Humiliation can also be embarrassing, but also still sexually arousing. Having someone masturbate while standing at their open windown, facing the busy street might be embarrassing to some, but it might also provoke that "oh my god what if someone sees me" emotion that others find so attractive in a sexual sense.

Of course being called a slut or a whore by someone you don't know isn't going to do anything for you, because there's no emotional attachment to that person. For many, someone in a BDSM chat calling them a slut would probably be lumped into the same category as getting cat-calls from construction workers as you pass by.

For dominants that know how to use it, and use it without it being or becoming degradation, it can be a great tool to get a submissive in the right frame of mind without a single touch.