"always adding that my comments should be ignored if OP doesn't like them" I think that's the difference between your comments vs. prompt hijacking. You're hijacking the prompt when you start making suggestions totally outside what the prompt was asking for and changing the prompt drastically into something it wasn't to begin with. I think if it's just details that are complementary to the OP's wishes that's fine, but you should always ask if it's okay with the OP that you're chiming in.

I really love some of the conversations that have been happening under prompts and how scenarios can be created, so I'd hate to lose those, but I think that stuff should always happen with clear understanding that it needs to be alright with the OP / the OP is taking part in the conversation.