The only risk I read about talking about suicide according to the lattest researches is sharing with others the method you used to take your own life.
Out of that, I read that it’s healthy to talk about it. Although, some professionals tend to avoid this topic.
I was always asked by psychiatrists, though.

I guess in the forums it happens to avoid other members feel affected because of others, many times, close contacts in the forum.
I once received in another forum a goodbye message by someone I had contact with and I had a time looking at the newspapers of his city to see if I can guess something. Thanks god, he contacted me after a time.
I don’t know what to tell you about this topic. What I’m sure is that the person who talks about his own suicide is the person who is struggling more and he deserves to be heard.