There's obviously a demand for NSFW content and even the more tasteful vtubers have fanservice moments here and there, meaning taking a prudish stance against it is a losing game. The priority should be setting firm boundaries. There is a difference between a streamer showing cleavage on their model vs. someone in chat talking about titfucking them, and it's important no-one in the community feels comfortable crossing that boundary. I fall into the lolbert opinion of "do whatever if I don't have to see it" a lot of people dislike because I really don't care for internet moral crusades about anything, but this is more a wider issue of basic human respect. Assuming women you barely know will be okay with sexual advances from strangers in their chat is creep behaviour.