It used to be that you couldn't discuss Sex, Religion or Politics.
Used to be. In the Olden Days of Yore. Now: "I like to bugger goats" is a perfectly acceptable introduction and no one is in the least offended by the title of Mr./Mrs Goat Buggerer.
Religion is essentially Child Buggery, which still seems to offend the majority, so bringing it up merely solicits agreement that it's bad, and on Politics everyone agrees to disagree.
But try and bring up "Science" or "Medicine" and see how quickly you're ostracized...I mean, just try it!