If I had to speculate wildly (oh nooooo not speculating-wildly, I hate doing that nooo...), the problem there is that they're discovering their mum getting fisted, not that you'd be willing to do that (maybe their mum is into it, not judging). Spending three minutes in a COD lobby will confirm the existence of people that want to fist your mum, I don't think anyone is particularly surprised in that situation (except for the people discovering their mum in the act of getting fisted and, possibly, the mum). I'm not saying this is a bad idea, I am in a relationship with someone who's sex drive is waaaaaaay higher than mine and being able to talk about that would be awesome! I'm just saying that 'society at large' is awful, and anything that doesn't align very specifically with broad cultural values of something being 'a problem' is going to be overlooked or dismissed as 'whining' or 'being ungrateful' or whatever other toxic thing. Hence why that community doesn't exist yet.