I think it is not limited to post WW2 Poland, as the issue of "assimilation" periodically resurfaced in previous periods. Consider, for example one of the best imho Polish writers Bruno Schulz who renounced Jewish community to marry a catholic woman, and of course his all writings were in Polish - and at the end he was killed by a nazi as a "revenge" against another nazi who protected him because he loved Schluz's art. However, his contemporary, Issak Bashevis Singer, who embraced the Yiddish culture (cf. _The Magician of Lublin_ which can be interpreted as being anti-assimilation) survived. Utter irony.
Based on the survey work that I am familiar with, the WW2 survivors were split between those who wanted to assimilate and saw socialism as a big chance, and those who were fed up with Poland and wanted to emigrate. One of the main factors cited by the latter was the Kielce pogrom - which was a particularly low blow after the holocaust.
However, the 1968 purges did not seem to have a similar effect. To my knowledge, people who left did so not because of "assimilation failure" but because they were fed up with the system and used that as an opportunity to get out. The folks from that period whom I met in the US were mainly of that sort, secular leftist and as the "magician of Lublin" neither Poles nor Jews. As one friend of mine aptly expressed it "I'm pro-Jewish when I talk to Polish Americans and pro-Polish when I talk to Jewish Americans."
However, the post-1968 Poland was remarkably free of any Semitic, or anti-Semitic innuendos. I knew many "assimilated" Jews (or perhaps descendants) who considered themselves anything but Jews, hippies, anti-authoritarians, or even staunch Catholics (go figure), you name it. In fact, I met only one person who openly embraced a Jewish identity, but my suspicion was that it was mainly for self-promotion (he was a budding poet).
I first encountered full-blown Polish-Jewish animosity when I came to the US - and I was quite surprised by it.
Wojtek