Perhaps I should amend that to "don't be obviously indiscriminate in a sleazy way". The bad thing isn't finding lots of people attractive, it's apparently caring nothing for them as a person (which is about having had no conversational interction with them before asking them out, some small amount of buildup is necessary, though as siduri says, if you're a decent chap, it's probably less than you think) or alternatively appearing desperate (which is about demeanor, I think). Things I've heard remarked upon have been bemusement at dinner invites following a dance with a stranger with no prior conversation, or demeanor problems.

If you actually like more than one person and have talked to the people concerned a bit, I don't see the harm.

(There's usually a niche for being the confident guy who flirts a lot with absolutely everyone: you get a name for yourself, but it's more as the loveable rogue than the creepy guy. That's possibly an advanced skill, though.)

Bonus link: only try these moves with a consenting partner ;-)