I believe it was Greg Jennings on Fox Sports that mentioned that he should've done this when the 49ers were an elite team and many considered him a really good QB at the time. I just couldn't take his message seriously as this started once he was sitting behind Gabbert as a backup QB. Plus, his ignorance with the Castro situation made me realize that he wasn't as educated on the matter as he should've been.
^^^Pretty much this^^^
If you are the starting quarterback, especially a really good starting quarterback, you can say whatever the hell you want. You will be considered anything from eccentric to "a man of principle who's in touch with social issues."
When you are the backup quarterback and you speak out, you're a distraction and there is nothing a football coach hates more than distractions. A backup quarterbacks' job is to stand there, hold the clipboard, be ready to go in if needed (hopefully never needed) and keep his fucking mouth shut.
Or as Crash Davis said: