How many other sporting events are watched by half of the country?
Your generalised statement is just plain wrong and these are just idiotic morons. The fact that they were out watching the game is totally irrelevant.
Yet we don't see these scenes in other countries with huge football followings. Germany? Nope. Spain? Nope.
We don't see it with other sports in this country.
When I was at uni I was friends with a Norwegian guy and he just didn't get it. He pointed out that people are smashing their things. Where's the logic? Utter morons.