The letter doesn't say they are more likely to make such content, but that the negative effects are more harmful to people who are already more vulnerable.
The whole first paragraph is completely overbearing. "Quick, pull in every non-mainstream group we can think of, and then describe them all as literally in fear of death from an ambiguous policy about fringe content. Oh, and of course all these people rent off landlords so nasty that they won't accept a single delayed rental payment and they'll end up homeless if that happens". It's completely indefensible hyperbole.