Did we establish whether this was a public or private school? He's four, so if it's a privately-funded pre-kindergarten then the school has every right to enforce an appearance code.
I know I probably have a really unpopular view, but there are going to be appearance codes throughout life. Long-haired men don't get the same attention during the interview process. They're not taken as seriously, unless they're in art or tech or something non-corporate.
I worked for Disney, and they have one of the strictest appearance codes on the planet. It's definitely been more relaxed over the last 10-15 years, but by "casting" and not employing, they can shuttle the long-haired, long-bearded me in one door and out the other. It doesn't fit with their image.
I say this as the wife of a guy who was a late-born hippie and would love to have long hair. He doesn't, though, because HR will say something. He won't do as well on interviews, should he choose to switch jobs. This mom revolting against the system now isn't going to change reality, which is that the kid will always be looked at differently by his teachers, peers, employers, etc, should this get that far.
I'm not some stodgy person who looks down on long hair. If guys keep it neat, it can look pretty presentable. But my perception has nothing to do with societal pressure, which is likely to be there for a very long time.
That said, I won't let my boys keep their hair long. I just don't like the look on little boys. So often, they look like little girls or the parents don't spend enough time combing it out so it looks unkempt. Or the parents get tired of caring for it and it turns into a mullet. And with the really little boys, it always seems less cute and more like the parents are trying to make a statement, which I think is part of what is happening in this story.
