Why should he be allowed to be a free agent and potentially join a team that plays against the Eagles?

They paid him, they should be able to NOT have him play for a different team.

It would almost be a beautiful thing if they could hold him for his entire contract, but keep him suspended without pay.

Then a few years from now when he is older and slower, he'd have to try and be a free agent then. Also, he could forget about any impressive career numbers after rotting for 4 years during his prime.