Everyone has a preference. Everyone has some style of hair cut they like the best (which can of course change at times).
The standards went from "shave it bald, everything goes" to "15 cm of length and up to 4 cm inches of bulk". And a lot of people's "ideal" preferred hair cut fell well within those parameters. And thus they've been lucky enough to just be able to go about their time in the CAF, wearing their ideal hair cut without any problems. Because they had an overlap between their preferences and the standards.
And not everyone was so lucky. Some people want hair that's coloured differently than allowed. Some people want hair that's longer than that. Etc.
But simply wearing your hair the way you want is not indicative of any mental illness, "attention seeing behaviour", or any of the other insulting assertions that have been constantly thrown about on this thread; dudes who like their hair shaved, and thus chose to shave their head aren't doing so because they're crazy; they're doing so because that's what they like, and they're allowed to do it.
How is it any different for coloured hair or longer hair?