But in this case, that's Blizzard's right. They own it whether you like it or not. Just because something is important doesn't mean they should lose property rights to it.
Abandonware is a thing and I remember there being some legal headway made recently in that respect, but Starcraft isn't abandoned. They just released a compatibility patch and made it free to download.
There's absolutely no chance in hell the dude saying he sent a copy to archive.org would have stopped those reddit threads from foaming at the mouth. People want the code, not the archive.
Blizzard does not lose their rights to it when somebody uploads the source code publically. If someone decides to use theor source code that they did not obtain a license for, blizzard can always sue.
Reading and learning from said source code is, and should not ever be illegal.
It's Blizzard's right, but only insofar as that happens to be what copyright terms say right now. Also, something having intrinsic value to society at large outside of the ability of a private entity to benefit from ownership is, quite literally, the reason why people should lose property rights to copyrighted works at some point.
It's their right now, but in "life + 70 years" it could have been an incredibly valuable cultural heritage in the hands of the public. Now the game will die when Blizzard chooses to stop adapting the game to new platforms.
Blizzard probably doesn't own all the source to SC1, they could have licensed code from other companies that they can't release even if they wanted to.
Intellectual Property isn't property, and publishing things does not deprive anyone of their property rights. It's a kludgy hack set up by Congress to prop
up industry.