Porphyrogenitus nails the problem caused by the "inner enemy" - the Westerners who themselves see Western culture as a threat to humanity:
European governments express concern over things like [Islamic militants in European countries calling for Shari'a in Europe], but if you judge real concern by action, it's hard to see much. We do not expect other cultures to tolerate movements dedicated to their destruction, but there is a level of passivity throughout much of the West to not only threats, but actions, based on that desire. I have written before that I am adamantly in favor of welcoming immigrants of whatever background who want to join our society and live within our civilization. But that is not the same as welcoming a viper to your bosom.
Fortunately, western civilization does not depend on Europe for its survival. If it did, western civ would be history by now.
The militant islamist jihadi movement possesses far more vitality than Europe, and islamism is a death cult!
European military forces couldn't fight their way out of a wet paper bag. They could spend more money on defense, but why should they? Their defense is provided by the country across the Atlantic, the one they all love to hate. This frees up their budgets to spend more on social programs.
There is nothing to stop the islamist tidal wave from rolling over Europe. Europe won't stand up for itself. After being rescued three times in one short century, the continent has come to expect rescue as its due.