well, i guess that as long as you dump your umds for your own, personal use you're not commiting any major crime (definitely nothing like distributing illegal copies).
in the end, everyone in the emulation community does that, including the jpcsp devs, since otherwise the emulator wouldn't have anything to run other than homebrews nobody really cares about. as far as i know a pc can't read psp's umd discs.
it's mostly just a word game, nobody's going to arrest you for dumping your own games and keeping them to yourself as a "backup".
in the end, everyone in the emulation community does that, including the jpcsp devs, since otherwise the emulator wouldn't have anything to run other than homebrews nobody really cares about. as far as i know a pc can't read psp's umd discs.
it's mostly just a word game, nobody's going to arrest you for dumping your own games and keeping them to yourself as a "backup".