Boys will be boys.
Boys want to prove something. Injuries happen. They are young, They will learn.
Let them get on with it and they can learn the hard way. If anything bad happens (I hope not) it has to stay on their conscience and they have to accept responsibility for their actions and the reprocutions that may arise.
Nobody really wants to get hurt, so when people have a go and do get hurt some may drop out and realise that its not really worth it.
To me it appears a bit of an ego thing brought on by the insecurity of not knowing whether they can actually defend themselves effectively and its a way of testing themselves. Don't get me wrong, it is good to have a good heavy sparring session every now and again but under controlled and SAFE conditions.