-- horrifying yes, but not the same as collaborating with the Nazis.
Also your statement about Poland was complicit. They quite happily turned Jews in or killed Jews themselves, is false -- some Poles did, yes, but there was no Polish government which did this, not even a mayor (well, Poland was to be wiped off the map according to the German plan) and the Armie Krajowe (anti-German and anti-Soviet partisan fighters) on the contrary fought anti-semitism.
So, some Poles were complicit, but not "Poland"
Not to mention that the Nazis planned to ultimately exterminate the Polish race through either Germanization or sterilization.
There is an interesting theory as to why Poles were singled out. Look at how the Nazis treated Slovaks, which shared fairly similar race and cultural traits with Poles, why were they for the most part left alone?
A theory suggests that because Poles and Germans lived alongside each other for centuries, there was much cross-breeding, and therefore while Poles were considered Slavs, many also possessed Germanic blood which would make them capable opponents, and that they were so anti-Germanic in their thinking that they would always be a threat to Germany if not completely wiped out.
Hitler never even considered treating Poland like Slovakia, allowing some level of autonomy. He was hell-bent on destroying all vestiges of all Polish language and culture.
One person who cleverly took advantage of Poland's hatred for the Jews was Bohdan Khmelnytsky. His Ukranians managed to get the Christians in the fort to kill the Jews also defending the fort. Then, Khmelnysky double crossed the Christian Poles after they killed their fellow Jewish defenders and slaughtered the Christians in the fort, too. There was also those Polish Cossacks in the 1200s who cut Jews open, put a cat in the Jew's body and sewed it up again. The Germans chose well in building the death camps in Poland.