@AuntieStella. I do think it is possible to deal with situations considerably more competently than seems to have happened here
Firstly, I'm sorry for your loss. As someone who's also suffered losses, I know it's very hard.
Facebook support groups for particularly confidential things always have questions before you join, and have done for years. If you manage a forum, that's different in approach, as people can arrive, and post, and then have to be gently managed out. I'm afraid that you project your own experiences here, because he never reached that stage. He says himself he was told that he couldn't join, because women would not feel comfortable. That was the extent of what upset him, and frankly it was the kindest thing that they could have said - it wasn't anything about him as a person, it was simply women wanting single sex provision to discuss their breasts, and their cancer. He's a man. It was as impersonal, neutral, and universal, as that.
I do see that you feel protective, as someone who worked hard to ensure nobody felt hurt by posts. Our mods are the same way. But telling someone at the questions stage that they can't join, with a polite and valid reason, isn't cruel. And having that stage, to protect all the existing members, is the epitome of competent.
@RufustheLanglovingreindeer
I'm so sorry. Words are completely inadequate, but I send much love.
@theflushedzebra thank God it was local (or regional?) recurrence. I'll cross everything that they have got it now, and she's fine. It's terrifying how many years later it can return.
@CharlieParley if you have a strong family history, I'd push for early check. An ultrasound is often more sensitive in younger women. I'm so sorry for your bereavements. 
Younger women get caught rather later, because we don't get mammograms. MRI and ultrasounds work better in young women, too, because we have denser breasts and mammograms don't necessarily work on us. Checking is vital, at this age.
I'm afraid in the present NHS you really do need to be your own best advocate. Only squeaky wheels get any oil.