The grandparent specifically rejected letting the Mario IP enter the public domain. So whether or not it should, that's a completely different discussion from the one being held here.
You can share a game you own even if it is still under copyright.
I'm saying there's a middle ground--or could be, if the laws were changed--where companies can keep their IP, but reselling and rent-seeking on decades old creations wouldn't be possible.
For example, 20 year old Mario games would be free for all to appreciate and preserve, but Nintendo can still get value out of their exclusive Mario IP, but only if they're making new games--and that's the important part, Nintendo would have to keep making new games, they can't just resell the same decades old games over and over.
That's the trade we make as a society. Copyright is a pretty big infringement on true freedom (think, anarchy freedom), but society gives up freedom to copy in exchange for people and companies creating new things. If companies aren't making new things, but are just rent-seeking, then let's end the trade and just let people be free to copy. Because we're not giving up our freedom to copy so you can rent-seek for the next 150 years, we're doing it so you can create new things.
You can share a game you own even if it is still under copyright.