I think consent is a large factor as to why those three things haven't been accepted yet. A mystery fourth option to your list could be rape. A child or animal doesn't have the cognitive ability to consent. A dead person obviously an't consent. If our grouping is of taboo sexual activity that doesn't require consent, then rape has to be in there as the most common practiced. Honestly, I'll never accept pedophilia, necrophilia, zoophilia, or rape. Without consent, it is wrong.
Maybe some people can get past this ick factor, but I can't.
I'm all for bjs.
