Please, just say what you really want. "Controlled immigration" would not have prevented this. But that's not what you really want. What you want is almost zero immigration. What you want is to refuse help to millions of innocent people who are fleeing from death and destruction. Because of what? Because of an incident, where a handful people was involved, and which would have been preventable, if the police had acted properly? Because of a few bad people you want to refuse help to millions?
You are not an average person. You can repeat it a thousand times, you can walk through the streets with your friends and shout "Wir sind das Volk" (We are the people), but you are not representative of the German people in any way, and you are not an average person. Because the average person in Germany is a decent human being, respects human rights and wants to help people who need help. Even if it is hard sometimes.