You would think that governments as well as people in general would understand that appeasing and rewarding negative behavior doesn't work. It's basic psychology 101--but one that not even most psychology professors understand or put to use. And apparently, this concept is foreign to many of the politically correct persuasion outside the classroom as well--for them, their feeling of moral "superiority" trumps human nature and causes liberals to turn a blind eye to justice and acts of violence.
In Bruce Bawer's new book, While Europe Slept: How Radical Islam is Destroying the West from Within, the side effects of the appeasement of Muslims by the Danish government are clear--as their government pumps more and more welfare money into the pockets of disgruntled Muslims, the rate of violence against "infidels" there increases.
It's an interesting problem, not just with Islam in Europe, but more generally. People tend to do what for which they're rewarded; in fact, I think you can look at it the other way, and in general figure that if there is some persistent behavior that you don't like, it's because there's some reward to it that you haven't recognized.
The problem with ever so much of what governments do, is that they tend to reinforce what they presumably want to reduce.