1. Stalin did not have the "entire" exiled Polish party leadership "murdered". Even the great god Wiki disagrees with this though it does say "almost" the entire leadership in Moscow were arrested and executed.
2. The idea that Polish reactionaries -- and I've met plenty of them in Poland and Britain -- would be the slightest bit concerned at the fate of Polish communists under Stalin -- is absurd.
3. The idea that the Polish party was purged by the Sovs in 1937 to clear the decks for the non-aggression pact with Nazi Germany in 1939 is equally absurd. Soviet offers to guarantee Czechoslovakia in 1938 -- which would have meant war with Nazi Germany and was vetoed by the reactionary Polish regime -- and the subsequent efforts to build collective security with France and Britain are well known and unchallenged.
4. The implication that the Polish communists and the Polish United Workers Party had no popular support in the immediate post-war period is also nonsense. The 1947 elections gave the communists and their allies an overwhelming majority. Even some bourgeois observers accept that the Polish communists had support from 50 per cent of the electorate whatever you may think about the way the election was conducted.
Finally, you say nothing about the roots of Polish reaction, the Catholic church, the nationalist resistance or the anti-semitism that was rife amongst their ranks. This is a complex issue as others on this forum have noted but the discussion should be based on facts and not anti-communist hysteria.
On a parting anectdotal note I met an old Pole in Warsaw in 1975 who was visiting relatives but had lived in England since the war. He was openly anti-communist but when I asked him about life before the war he told me it was like living "in the jungle". I didn't understand so he explained that life before the war under the Polish dictatorship was absolute misery for working people " a land where dog ate dog" he said.