You have your opinion and I have mine. And that is the problem, they are only opinions! There is no proof either way. There are reports and statistics that suggest both opinions could be wrong.
As for my comment about kids not having good memories about baseball. I am saying that an average pitcher that doesn't throw a curveball will likely not pitch past 12 years old. I have seen this many times in my area. If they don't have some success, then they will quit before they even get to high school.
I coach a 10 under baseball team. I haven't taught them a curveball yet, because I want them to learn and trust their fastball and change up first. I will probably teach them a curveball within the next couple of years. Not because of my desire to win, but I want them to learn to throw it correctly and trust it during game situations. I won't let it become their #2 pitch, it will always remain the third choice behind the Fastball and Change up. I will likely let them throw it only to get out of a jam and I will set a maximum number per game. As long as they are supervised and instructed on how and when to throw it, then I honestly don't see any problems with it.
With that said, I do have a major problem with those coaches who let their kids throw them incorrectly(supinate).
As for supinating when throwing a curveball, at least we both agree on something.
Take care.