That was Stalin's doing, he drew up the maps for Eastern Europe after the war.
Stalin is a very useful character. You can blame him for everything and expect others to believe.
Still: 1) it wasn't Stalin who threw stones at the Germans being herded from Pomerania, 2) Other WWII allies agreed to the Stalin's proposal, making them allies's, not Stalin's decisions.
I don't want to whitewash anyone in that situation, the Germans themselves had given enough reasons for the hard sentiments. And Russians too, of course.
Nevertheless, any attempts by today pampered arm-chair self-declared moralists to judge the WWII vets and survivors are laughable.