Distributing roms of games under copyright which you don't have a specific licence to distribute from the copyright owner is illegal.
So if you don't own the original arcade board then the roms you have are illegal. Even when you own the original games, the sites that host them don't have permission to distribute them so they and you are acting unlawfully by offering or downloading the games.
In the real world considering the comparitively small numbers of people that emulate and the fact that these games are no longer available for sale commercially then so long as no one is actually selling them or making money from them, for the most part (at least as far as end users are concerned) copyright owners generally turn a blind eye.
But it is illegal to own or use copyright roms without permission, so in reference to that, this sites rules are there for its own protection.
The forum rules state explicitly that we don't discuss romsites, links to romsites or how or where to obtain roms. There is no grey area or debate, just don't do it.