I think this is a nice idea, I really hope I can say what I want to without using any politically incorrect terms, I have no desire to be offensive or upset anyone if in my own naievity I say something out of order.
I do think people who have come to terms with their own sexuality, or who have never had any issues with their sexuality will still post in the main topic areas. That probably also applies to all your target groups. Of course it is totally possible to post on the main forum without ever actually sharing any of that information.
Maybe the people that you are trying to encourage in the sexual or gender oriented group may be afraid to post because of the "open forum status" and being discovered by friends, family or work colleagues who had no previous knowledge of their own individual personal life, either their sexuality or even that they have PCa.
So having the conversations open to all will inevitably get some readers or contributors who are not entirely genuine. I would love to think that the vast majority of forum members are sensible enough, even if they do have any prejudice, to just stay out of those conversations but sadly I think that may not be the case.
Also Many of us regular forum members use the recent conversations tab to keep up to date with our friends and fellow members, I know that I for one, never actually look at the topic just what is said in the post. To me the poster's sexual orientation, gender, age, race or religion is totally immaterial as long as their purpose is to seek help or support on anything to do with any aspect of PCa.
Defintely worth trying as I am sure many people do miss out on some very valuable support especially if the questions or support they need are really best answered by someone in a simialr situation to themself.
All your hard work is very much appreciated