Another unpopular opinion: While the post-World War II mass expulsions were morally questionable, they also helped create more stable borders than existed in the aftermath of World War I. While Germans were furious as hell about the Oder-Neisse Line for decades, they also eventually accepted this line once the older generations of Germans began passing away and younger generations of Germans with no memories of this line began rising to positions of political prominence. Ditto for Germany giving up its claim to the Sudetenland. I guess that good fences really do make good neighbors, eh? 
As a side note, the demographic issue would not be too severe even in the extraordinarily unlikely event that all of the expelled Germans and their descendants would have subsequently returned to Czechia and Poland. In such a scenario, both Czechia and Poland would have become about 20% German right now, but this wouldn't be a minority percentage that's impossible to handle, especially considering that the Germany of 2022 is much more well-behaved than the Germany of the late 1930s was. A Ukraine that was almost 20% Russian did experience a lot of problems starting in 2014 due to a more problematic neighbor, though.
As a side note, the demographic issue would not be too severe even in the extraordinarily unlikely event that all of the expelled Germans and their descendants would have subsequently returned to Czechia and Poland. In such a scenario, both Czechia and Poland would have become about 20% German right now, but this wouldn't be a minority percentage that's impossible to handle, especially considering that the Germany of 2022 is much more well-behaved than the Germany of the late 1930s was. A Ukraine that was almost 20% Russian did experience a lot of problems starting in 2014 due to a more problematic neighbor, though.
