The core precedent is old and stable: writing software that mimics a console is lawful, and US courts said so decades ago in the cases that let early PlayStation emulators live. Clean-room reimplementation of a system is not infringement.
What was never settled in emulation's favor is distribution. Downloading a game you don't own is straightforward infringement everywhere that matters, and hosting collections is what actually gets projects and sites shut down. The emulator survives; the ROM site doesn't.
The honest personal-use position: emulate systems you own, from copies you made, and treat 'abandonware' as a moral argument rather than a legal one — because courts consistently do.
