Kaepernick would be the best QB on my favorite team if they signed him today. It seems almost certain that if he is truly looking to play and be a backup then the reason he hasn’t been signed is his political protests.
But perhaps “blackballed” needs to be better defined. I’m not sure that there is actual collusion going on as opposed to teams simply believing individually that he would be a distraction and bad for their brands.
And I’m not sure that this is necessarily something bad. Certainly if I suddenly decided to start engaging in public political activism while on work time and in uniform at my place of business, in a manner that offends and alienates a significant portion of my company’s paying customers, it would not be reasonable for me to then complain when my employer finds my behavior objectionable and looks for someone else to hire.