Are emulators bad?

[nybergh]

I read the game forum guidelines where the following is written by our old friend Mr Jones.

Don't ask for, or advertise, ROM's and Emulators , no matter how old, it's still bad....

Why? Just of curiosity: Are emulators illegal? I use an opensourced one called DOSbox (<=moderators, please note that I didn't link it ) to play old lucasarts and apogee productions and I didn't know it damages the owners of the games that I'm able to play their games 10 years later...