Right before 3e came out, I was running a 2nd edition game using just the PHB, DMG and MM, and it was great fun. Yes, 3e is by far a better system, but that doesn't mean all those games we ran under the old system suddenly sucked. So, why not?
That said, I would have to question why the game was being run under 2nd edition in the first place. If it's a new game, I would strongly advocate for using 3rd edition, or even another game entirely.
Interesting- the general opinion seems to be that, whatever its faults, 2e had great settings. I have to agree- I loved Spelljammer, Darksun and Greyhawk, thought Ravenloft was okay and never really got a chance to play some of the other settings, like Al-Quadim or Birthright, that I really think I would've liked.
The DM would have to be incredibly hot. And naked.
Seriously though, there are easier game systems from that era to use - so I'd use 'em. It's not that I dislike 2E, it's that it's not the best tool for the job anymore and if I were going to play D&D without d20 I'd have a specific purpose in mind and be looking for specific sorts of tools in my ruleset. Without a lot more thought though, I can't come up with a single reason that I would fall back to the less easy to use ruleset when I've got an inprint and magnificently approachable edition to press upon my players. Even if I were going to try to resurrect some of the more noteworthy 1e/2e settings I'd probably want the extra mile of revamping those settings for another ruleset rather than the previous editions. OTOH, I already played in most if not all of thsoe settings more than once many times over the years - I don't know if I need to revisit them.
I mean, just because its old doesn't mean I think anyone should be breaking out their Cyborg Commando boxed sets and running a game with the notion that they're being coll and old school.
unless it is a planescape campaign i don't think i would play 2e, i like the 3e rules better and i'm more used to them. the 2e rules are complicated and fustrating and the 3e, while still complicated enough to satesfiy me are much simpler to play with. on the other hand any setting or system could be good if there is a good dm and group, so if this was the only choice then i'd rather play 2e then not at all.