If the friendship is obviously a very personal one, i.e. you've been invested in each other for a long time, then I believe ghosting is abuse. Whether it's someone doing it to you, or whether you're doing it to them, cutting someone off completely and refusing contact is awful. Although I'd understand if the two people didn't know eachother very well, or if someone legitimately did not feel safe.
So... even if you really don't like somebody, don't be cruel. Allow them to express themselves to you. You don't have to say much back, you don't even have to agree with them. Too much damage can be done to a person if you ghost them, especially if they are emotionally unstable or fragile. They will come to realize that it's futile and they'll move on.