If Poland's independence was at stake I'd understand that, but he basically did it for money and who knows might have done it to a free democratic Poland also.
An interesting question - did he work in any way for the USA after 1989? I suspect we won't find out the answer to that, but it could be interesting to look at potential links between him and the AWS government in Poland. As I recall - the Americans were pushing the parties into the AWS coalition - and his visit to Poland (with his sudden right-wing feelings)..hmm.
Enough there to make you wonder if he really was on the Polish side, at least.
Why he could be hated ?
From a left wing point of view, he could be seen as a spy and traitor who betrayed Poland for the sake of easy cash.
From a right wing point of view, he betrayed Poland as an very senior army officer - and the army was always strongly associated (not so much now, I don't think?) with the identity of Poland. He was also (obviously) a very senior communist - so enough reason to hate him from a right wing perspective.
Well, do you have sources to back it up ? I think that he did it for everything but monies!
I can only say one thing - his son suffered a mysterious accident while sailing. Sailing isn't exactly a poor man's hobby...