When I first started following the NBA, in the West-Baylor-Chamberlain-Russell-Oscar Robertson era, the league wouldn't accept most underclassmen unless they could be proven to be a hardship case.
Maybe I have a rose colored memory, but it seems to me that the NBA was a very highly competitive and more entertaining league back then.
College basketball wasn't that competitive in that it seemed to be UCLA, and everyone else a distant second.
I do have difficulty in saying that any young man can't go to work in any job that might be offered to him. But I still think that in spite of the likes of Moses Malone, McGrady, Bryant and even King James...the league is better off with this rule. I would have made it age 20, and 2 years out of high school.