Hate to jump in the fray on this, but this argument is absurd.
There is clear data that suggests that the younger a player enters the league, the better the chances are he will have a succesful career. That is irrefutable. Any personal feelings you have on the subject aren't relevant when looking at this data.
The success rate of high school to pro players is significantly higher than the rate of college players drafted into the NBA. Again, this isn't opinion, it is a fact.
The argument that KG, Kobe, etc.. weren't as succesful at 18 as college players as rookies is also a flawed argument. The entire premise of the article Kerr wrote is tied to this (false) notion that college does a better job preparing players for a NBA career than time on a NBA team. If that were the case, KG, Kobe and other high school to college pros would still be struggling with the challenges many rookies face in their 3rd season, correct? We should be comparing how rookies (average age of 20-21) compare to third year HS players. Both had two years to "prepare", either in college or the NBA. For the record, Kobe average 19.9, 5.3 and 3.8 his 3rd year. KG averaged 18.5, 9.6 and 4.2 in HIS third year. Heck, Kwame Brown, everyone's prime example of a bust, averaged 10.9 and 7.4 rpg his third year. Seems to me that two years in the NBA did a great job preparing these players.
Look at the Boston Celtics this year. JaJuan Johnson and E'Tuan Moore were both 4-year college players at Purdue. They haven't contributed a bit all season. Avery Bradley on the other hand? He played one year in college (where he completely underwhelmed) and then rode the pine, hard, his rookie season, including a stint in the D League. Funny, one year playing behind future Hall of Famers like Ray Allen and Paul Pierce prepared Bradley for a breakout season. You really think another year with Rick Barnes would have left Bradley contributing to a conference semi-finalist team? Find that VERY hard to believe.
NBA teams have resources college programs can only dream of. Expansive coaching staffs, private chefs, nutritionists, huge training staffs. With no classes to worry about or NCAA restrictions on practice time (or girls volleyball limitations on practice time), young players have the ability to focus solely on their JOB; basketball. The ability to spend all day, every day, focused only on getting better (with all of the appropriate resources around them) allows for players to do just that, get better. Throw in the ability to learn from experienced veterans who know what it takes to be succesful and I'm not sure how anyone could suggest college is a better learning environment from a basketball standpoint. Would you rather spend two years in a locker room learning from Hasheem Thabeet and AJ Price on how to succeed in the NBA or from NBA veterans who have actually done it for a decade? You can cherry pick high school players who struggled dealing with the NBA lifestyle, but I can find many more who went to college who had those same struggles.
You are obviously entitled to your own opinions on this topic. However, the data suggests that Kerr's argument (and yours, to a point) is backed up not by statistics, but rather, personal feelings. I'll take data and history.