Nobody asked the Silesian Germans if they wanted to leave. They either expelled them or raped/killed them. This is actually not a very nice part of Polish history, I wonder if the Poles consider their behaviour towards the Silesian Germans in the post-war years still as being justified or do they look back at this episode in shame?
I don't believe there is much to be ashamed about. Most every nation in history has performed some form of ethnic cleansing. Berlin thought nothing of cleansing traditional Czech and Polish lands and replacing the people with ethnic Germans. What Poland did is also no worse than what the Russians did, stealing Konigsberg from the Germans in East Prussia and transforming it into Kaliningrad. The difference between the two actions is that the Russians stole a historic German region. Poles reclaimed a region (Silesia) they had a historic right to.