Very often, the most popular answer may be dead wrong. Like Colibri says, this system sounds like a great way to use crowdsourcing, but often fails. A lot of us “know” things to be true that aren’t. For the curious, Lies My Teacher Told Me is shows a number of examples of this phenomenon. That’s presuming everyone voting is doing so in good faith. What happens when the voting concerns a thread like the paranormal ones?
And yes, I’m sure Dopers think that they will weight the popularity of the answer as not being necessarily “correct,” but GQ is the place where we have the most new Dopers and the most short-term guests. If they see an officially-certified THIS IS THE ANSWER icon without knowing the limitations, how does that serve anyone? And aren’t those the folks most likely to want to look for such an icon? In other words, it will deceive those that are most-likely to be looking for it.