It's the reasons why they vote that make the youth a peril. As has been said, they are inexperienced and filled with idealistic fervour. Bad combination and often the reason why ships that sail out into choppy waters with high aims get wrecked on the rocks of reality before long. It's important for any culture not to allow the inexperienced to be so dismissive of their elders. This has never been the human way and as America has created the eternal teenager, aged between fourteen and a hundred and fourteen, things have become unpredictable.
If no one wants to grow up anymore and is always on holiday and just wants to buy the world a coke, then the future will be a set of nasty rocks sticking up out of the sea of tranquility that is believed to be the reward for loving everything with a pulse.
Tories had no counter to a man who could literally offer the naive the world knowing he would not have to carry the promises out.