Not really free. Stop paying for PS+ and they are gone. Xbox gold actually gives you 360 and Xbox games. They're yours even if you stop subscribing to Gold.
I knew someone would bring up the "not free" argument lol
While I agree with you to some extent since I don't have permanent ownership of the games, to me it feels the same as free since my mindset is that I'm paying for the ability to play online, and the games are just a bonus. I'm going to pay for PS+ to play online regardless of the "free" games.
Also I'm not going to replay the PS+ games after I finish them since there's already a massive backlog of other games I haven't played yet, so it doesn't even matter if I have access to them forever. I've been a PS+ member for years so I don't really think about the "what if I don't renew the subscription" situation either.
There's really no sense in arguing this anyways, but I think it might be better to think of it as Sony allowing you to experience the game for free in return for paying to play online multiplayer. The term "free" doesn't necessarily mean being given permanent ownership of something.