I'm gonna call bullshit on that. I think it's intellectually lazy. What people really mean by this is that the only good opinion is one that has been carefully considered, and that's certainly true, but simply adopting a "moderate" or "middle of the road" position isn't the same thing. It's a cheat, and it's no substitute for actually thinking.
I'll also point out (and you knew this was coming) that I think this is a device used more often by the Right these days. "Fair and Balanced," right? The GOP is the voice of the infallible "center" and those crazies on the Left are insufficiently moderate. This is the single most boldly marketed message coming from the Right these days. The pronouncement of their supreme even-handedness.
I've seen a lot of ads on the Metro lately listing the most extreme circumstances under which abortions occur, and asking if abortion rights have "gone to far." That's just the most disingenuous load of crap. Those people aren't concerned that we've "gone to far". They are simply trying a slight of hand to distract the public from their extreme (yes, extreme) agenda in which no woman has the right to an abortion.
OK, I could go on, but I'm beginning to sort of ramble around the issue here.
Anyone wanna argue with me? I'm truly very interested in contradictory opinions (how moderate of me!) because I am still trying to solidify this concept in my mind. And hearing other peoples' thoughts is one way we liberals inform ourselves, ya see.