I would imagine it was originally a hygiene issue as it has a low prevalence outside of hot countries other than possibly the USA. Today it is not such an issue but many parents still prefer their son to have a crewe neck rather than a skivvy in the belief it is more hygienic rather than for religious reasons. I guess the debate gets down to what is the limit of parental control over what they perceive as best for their sons. Or does it get down to nature always gets it right and there should be no interference?