I would argue the problem is merely of the scale of crazies. Granted, a lot of the European democracies are doing a lot better than the US or UK, but at the same time, fundamentally, no system other than a dictatorship that actively acts against its own people can withstand a large enough population that vehemently decides to be evil. Israel's parliamentary system is a pretty good example. On paper not a bad system, the problem is that so many of them are completely captured by the right and far right that even the leftmost parties are still pretty damn horrendous when it comes to the West Bank and Gaza.