What subject you would never give quarter to for maybe being at least partially right, because it is a subject you are dead against, even to discuss?

There are subjects people just refuse to discuss or give any merit to as being right, even in the smallest bit. They do so because the comment, question, issue, subject, etc. fall in their ”adamantly oppose” range. What falls in that range for you, something you do not even want or care to explore to even provide a chance there might be some truth in?