Depends on the thread. If someone is asking for an honest opinion and I don't want to be swayed by all the other opinions, I'll go right into giving my opinion and then read the rest to see how many others agree or disagree with how I see things.
If a thread is 5 pages long? I might read the first two pages, maybe a little of the 4th or 5th, and then give my opinion.
Looking like a idiot isn't something I typically concern myself with on message boards.