It's legitimate in that is is a chat-room blog, it is illegitimate in that what transpires on this blog is the farthest thing from "sleuthing" or crime solving that I can think of.
Most people on the site are unfamiliar with detailed facts of the cases, or with forensics. There are regulars who roam from forum to forum in zombie-like fashion, espousing the exact same thoughts over and over again, regardless of the case or topic.
There is also a lot of claim to expertise or relevant profession that is supposedly vetted by Websleuths, claims that seem doubtful. If someone says they are an attorney, that alone does not make them qualified to speak to just any legal issue. And any attorney not afraid of a law suit would make this full disclosure upfront. Yet none of the so-called attorneys on the site do this.
And if someone presents themselves as an expert or practicing professional, why aren't others on the forum allowed to know what actual qualifications they have and who they are. It's one thing to remain anonymous when you are simply giving an opinion-but when you claim your opinion is based on experience or education, I do believe at that point you should be prepared to reveal yourself, so that people can know the quality of the information they are relying on.
Websleuths is a real chatroom blog, but it is a sham as a place of fact and substantiation.