Shaman Tanking

WTH. I've seen several people now discussing shaman tanking, and not to take away from their achievement, but why would you want to?

To show that it can be done? Big deal. With enough heals, I've seen warlocks with enormous health "tank" adds. Doesn't mean that I'd want them to, or call them a tank. Just because you can hold a mob for a while, doesn't mean you're a tank. If I wouldn't take a warrior with similar stats as a tank, why would I take a shaman?

I just don't get it. Some say it's for the challenge. Go grab a mage and tank. Or is that too much of a challenge? How much challenge is just right?

Maybe it's just that I'm not "thinking outside the box." But from experience, when one class starts doing something that it's not intended to do, Blizzard comes along and fixes it. So more than anything, I'm probably against such things just because I don't want anything "fixed".

Just my opinion.