I've never heard anyone argue that lifting wouldn't stunt your growth. If you're as tall as you want to be, or you're already into your twenties, it's probably not going to hurt anything. But heavy workouts do stunt your growth if you're still in your growing years.

There's nothing complicated about it... working out tears down muscle tissue. Your muscles recover and rebuild. That recovering and rebuilding uses up the same energy that might otherwise be used for growth spirts. And the added tension and strain on growing or underdeveloped bones and joints can do irreparable damage.

It's the same thinking that makes a Veterinarian tell you not to let large breed dogs get too much exercise when they're still growing.