I don't think dating someone you don't have a long-term interest in is mean.
Dating is just dating. It's not matrimony. There are no promises or obligations.
One point of dating is just to have a nice time together. Just some companionship. Someone to go to a movie with. Just to be friends and maybe even smooch a little. Nothing wrong with that.
You might find, by dating someone you think you are not really into, that actually you really like them. Or not.