he's been good (really good in fact) and he's been not so good in his fairly short career.
He's still young, and I don't know if he'd be good or not, but saying he's bad or would be bad definitively isn't true at all. Maybe he'd be bad. Maybe he'd be good. But his career stats show that he's not as bad as people are making him out to be in my opinion.
http://www.nfl.com/player/colinkaepernick/2495186/careerstats
And certainly better than Tom Savage. I get that there's more to signing him than just QB play, but like any news cycle, after the initial backlash (what exactly would the backlash be though?) it would die down soon.
The biggest mistake the NFL did (or NFL teams) was to not sign him and get him into a camp to start the year. If that had happened we wouldn't be talking about this right now, whether he made a roster or not. He would have had a chance, and that would have made a huge difference in the dialogue.