Germany has massively risen in power, both political and economical. This is partially due to political mismanagement/corruption (esp. Eastern Europe), but a huge part of the growth of Germany results out of the loss that has been paid in poorer Europe.
And, surprise, both foreign countries and the German left do not like this.
That, and conflict in which aggressor aimed to physically destroy our population followed by half of century of being colony for USSR also had its part in our economies. When 90's finally came we had few people that remembered democracy and even less businesses that could kickstart our economies, only massive debts inherited from communist goverments.
I suspect that on a certain animalistic level, the "message" that the protestors want to get across (to Merkel and people at her level) is, basically: "Do what you have to do. But don't pretend to feel that there's anything dignified and civilized about it."