I think this is one of the circumstances where if he took the opportunity, it wouldn't be consider favoritism but rather of a strategic necessity considering how John Mccain's admiral father's decision making could be compromised by any risks such decisions could have towards his son's welfare.

Of course there are way more variable involved, but I think his refusal was mostly on the basis of maintaining solidarity with the other POWs. In that situation, I could imagine that one of the few things that would keep me going was knowing that the thing i was fighting for back home wasn't just a delusion.

If the other POWs saw Mccain released for on political reasons, then who is to say that the POWs loyalty to their nation wouldn't have been compromised?