A "roast" is typically when people who know you well are making fun of you or saying things they normally wouldn't to you / things other people say behind your back. It works because the people doing the roast, and the person being roasted, know each other well enough not to have hard feelings about what's said.
Few, or no, people on this board probably feel like they "know you well". Without that, it's just a bunch of **** talking and flaming, and honestly it's not really funny.
That's why everyone is saying it's not a good idea. Because the people on here who do feel like they know each other well enough for something like that, are already doing it to each other anyways. This just comes across as a grab for attention, especially when it seems like you're getting upset that people aren't paying more attention by agreeing to play along or write you a long reply why not.