To be fair, it’s software specifically designed to run digital backups of what’s supposed to be personally owned media. It just so happens that it’s very easy to obtain a copy otherwise, but there’s nothing inherently illegal about it or the games.
Strong arming independent projects, and individual developers especially, that are very careful to not endorse that, effectively holding them accountable for others, is morally questionable at best.
From a theoretical point of view, emulators of modern consoles may actually be illegal. Under the DMCA, emulation for preservation is protected as a periodically-renewed exemption list defined by the library of congress. But, (paraphrasing) “creating or distributing any hardware or software device—or component of such—designed to circumvent DRM technology” is still illegal irrespective of any exemptions. A reasonable (and bullshit) interpretation of that means that any emulator which is capable of bypassing any DRM features (such as decrypting ROM using user-provided keys) is a violation under the act.
I say theoretical because it hasn’t ever actually been tested in a court. Nintendo v. Tropic Haze LLC nearly gave us the answer, but the latter chose to settle instead.