There [i]is[/i] no taboo subject when it comes to being an author. There are taboo subjects for readers, however, which is entirely different. An author has the freedom to write about sex, racism, murder, genocide, slavery, rape, jaywalking, etc. They have that freedom and it is actually a service to the public that such things are discussed. I find it absolutely reprehensible that things like Tom Sawyer have been yanked out of schools, though of course that is a "reader's" choice and not the author so it's somewhat different. It is all up to the writer on what they can or cannot put in their book. If a modern black African wants to write a book from a 13th century Mongolian's perspective, he can and should if that is what he wants to do. There is no 'story you cannot write' or 'story that isn't yours to tell.'

When it comes to an RP however, it's simply up to what you and your partner are mutually, consensually comfortable with. That and you also need to follow the Guild guidelines if you write it publicly. I think being 'tasteless' is how you write something rather than what you write. For instance, smut can easily be tasteless if done incorrectly. But if done correctly it's a nice experience if you do it with someone you trust (or don't, whatever floats your boat).

I think the only subject matter I condemn as 'taboo' is misinformation and lying in order to spread an ideology, even if it is a harmless one. You can, of course, spread the truth or embellish if you're writing a novel. But using said novel to intentionally spread information that is false, particularly if it is harmful, is a cardinal sin in my book.