I was taught, and do believe, that you shouldn't speak ill of the dead, if only because they can't answer back.
I agree, the time for the "you idiot, what do you think you're doing!?" type comments belong at the point where you are e.g. trying to take the keys out of your drunk mate's hand before he drives off, if they belong anywhere at all! After the event, all that's left is respect for the deceased, and finding out what went wrong.
Having said that a sober discussion of events leading up to a tragedy, bereft of personal attack, can be of use for all sorts of reason. Who knows? A well placed thoughtful comment on here might encourage someone NOT to go out and kill themselves through bad judgement.
On the subject of responsible posting. Well, internet forums are all about annonymity, aren't they? You might as well ask people to stop using the web to download porn.
RIP is what you write when you want to convey the bare minimum of sorrow, imho.