I tend not to take a strong stand on something that I don't know A LOT about - this approach has worked well for me and saved me much embarrassment.
If I know what I consider to be "enough" about an issue (through formal education, personal experience, etc.), I will take my stand and defend it to the best of my abilities. If it is just my OPINION, I will treat it as such. Treating a personal opinion or an anecdotal event like Gospel Truth is what gets a lot of folks in deep water on the wrong side of intellectual debates, IMO.
Oh... all of this should be assumed correct, because I said so! [:D]
edited to add:
Sorry, I didn't read read Tex's response above before posting mine. He essentially said the same thing, but more succinctly. I should have just pointed up and said "ditto." But I have never been accused of using too few words - if it's worth talking about, it's worth talking to death...