Everyone operating under the assumption that you only need one good quarterback in the league. Check out the guys starting at the end of the season versus the ones who started at the beginning. Pretty high percentage of teams in the league had a different starter. Or used a different one during the course of the season.
There really is no downside to adding Tebow. The cost will be negligible in terms of assets, probably nothing. The guy has a better winning percentage than either QB on the roster, and is the only one to have a playoff start. He is 25 years old, an age when most QBs are just starting to come into their own. He has the size, athletic ablility, and mindset to play other positions. Tim could probably do a decent job at middle linebacker in a pinch. What's to lose?