It has much to do with History, the oprressed becomes angry and then because living in Poland in the last 300years have been quiet uncertain times, when you are not sure if it is worth working honestly for something, because people have it in their brains that next thing the political system might change or maybe a war , and they can lose it all...
The oppressed you speak of died a long time ago. No one to my knowledge is even close to 300 years old in Poland. Poles were not the only people in the past to experience war. Modern day Poles need to give up this shtick.
It's weird, while I was living in london, the only people I heard Poles complain about in regards to stealing were other Poles and it wasn't an isolated thing. That being the case perhaps there was another reason for this. Maybe cultural sensitivity, maybe expecting more from their countrymen, maybe they just had more frequent contact with other Poles thus skewing the probability of theft in one direction...