The welfare state diminishes personal responsibility; diminished personal responsibility creates a debased and feral underclass.
Moral relativism denies common standards of civilised behaviour; no culture can survive without common standards of civilised behaviour.
Multiculturalism encourages intellectual dishonesty to flourish; intellectual dishonesty makes it impossible to admit error or to learn from experience.
Systematic euphemism (political correctness) substitutes form for substance; an emphasis on form over substance is the defining characteristic of stagnant societies.
The consequences of all the above have achieved critical mass in modern Britain.