If you just want to shut a discussion down at work, it is usually possible to frame the request as "I find this topic difficult and would appreciate it if you stopped bringing it up, as a favor." I've done that with things that didn't have a real-world moral valance (I had to ask one coworker at old job if we could not discuss Donna Noble's Doctor Who story arc because his takes were so bad, and he clearly thought I was off my rocker but he also never brought her up again).