I am willing to bet that effectively every single MAME developer has pirated one or more ROMs at one point. Infringement is infringement. The "they don't distribute it with ROMs" is a red herring if those same people are themselves pirating ROMs.

In order to make the game work, they need the ROM and/or CHD file. I doubt every developer has gotten the rights to license the ROM etc and just pirated it to get it to work.

In the late 1990s people used to earn money selling MAME CDs with the ROMs on them. People thought they were getting legit ROMs, but it was just more pirating.

StarROMS sold some Atari ROMs and I think it was legit but they got shut down.

If only there was some sort of system that sells ROMs legally and gets permission to sell the ROMs and build it into MAME or MESS so each ROM or Floppy can be bought and the original ROM developers make money from the sales. But such a system isn't in place so most get their ROMs via piracy.

So are you arguing that people shouldn't even attempt to emulate older hardware, or that they shouldn't worry about the law when doing it?

My feeling is they should remember that they are still handling pirated material - even though using it these days might as well be considered a zero risk.

With the future open-sourcing of MAME this stuff will be everywhere. And, unless you're playing Roto or Gridlee, you're most certainly handling pirated material. Doesn't matter if it's on your local hard drive or archive.org.