... Star Trek portrays humans in relationships which are basically beastiality (humans mating with other species)
Beastility is people having sex with animals, that where you get the "beast" in bestiality. Which of Trek's intelligent species do you believe to be "animals?"
... thus a society which accepts that ...
I never considered this before, but given how Vulcans feel about Humans and non-Vulcans in general, I wonder how they felt about Spock?
A contaminate in the Vulcan superiority?
I think we see lots of hints that both versions of Spock is looked down upon by "pure" Vulcans.
The strongest examples I can think of are Spock being bullied by Vulcan children who make racist comments about his human heritage, Sarek seems very concerned that Spock be Vulcan. Why would it be so bad if Spock were more human, like his mother? I always found it hard to like Sarek completely because of his attitude towards Spock. I find Sarek interesting and charismatic, but not always likable.
There's a big storyline running thru Enterprise about Vulcan/human relations, and how the Vulcans treat humans as needed their custodial control for their own good. On ENT, Vulcan attitudes towards humans are seen the way a weary parent handles a rebellious child who needs to be controlled to stop them from hurting themselves. That relationship does evolve, and it's clearly not the same as it would be in the 23rd and 24th century, but it's the strongest look we have at human/Vulcan relations.
Have you seen Enterprise T'Girl?