Cooper Rush is an unknown, but I know Kaepernick can't cut it. It's not ridiculous at all to say I'd take Rush over Kaepernick. I'd do it every day of the week.
Here's a list of backups that Kaepernick is either on par with or possibly better than:
Matt Cassel, Titans
Kellen Clemens, Chargers
Kellen Moore, Cowboys
Scott Tolzien, Colts
Sean Mannion, Rams
Jake Rudock/Brad Kaaya, Lions
Ryan Griffin, Buccaneers
Trevone Boykin, Seahawks
Geno Smith, Giants
Matt Barkley/CJ Beathard, 49ers
Here are the ones who I'd take over Kaepernick:
Jimmy Garoppolo, Patriots
Matt Moore, Dolphins
Trevor Siemian/Paxton Lynch, Broncos
Colt McCoy, Redskins
Deshaun Watson/Tom Savage, Texans
AJ McCarron, Bengals
T.J. Yates/Cardale Jones/Nathan Peterman, Bills
Mitchell Trubisky/Mike Glennon, Bears
Chad Henne, Jaguars
Drew Stanton, Cardinals
Kevin Hogan/Brock Osweiler/DeShone Kizer, Browns
Chase Daniel, Saints
Derek Anderson, Panthers
Nick Foles, Eagles
Ryan Mallett, Ravens
Case Keenum, Vikings
Bryce Petty/Christian Hackenberg, Jets
Landry Jones/Josh Dobbs, Steelers
Patrick Mahomes, Chiefs
Connor Cook/EJ Manuel, Raiders
Matt Schaub, Falcons
Brett Hundley, Packers
Some of those guys I'd take over Kaepernick because of youth, potential, but the point remains. Kaepernick has no value in the league. He's not even better than most backups.
And he turned down a backup gig.
He's a third string QB on many teams. Who wants to put up with that?
It's not blacklisting or discriminating. You're a low end backup talent. No one wants to put up with questions when you suck. And of the small number of teams who might have been ok with it.... you turned them down.