You are confusing Religion with fun. Each has its own place. What's wrong with having fun. (0..0)
It is a bit difficult for some people to have fun in the days leading up to November 1st. It is even more difficult to have fun the night before one lays flowers at the grave of close relations.
Another point is that Halloween, as a celebration, is new to Poland. And many people just don't get it.
If some families choose to visit the cemetery the day before Nov 1st... then you can forget about Halloween.
So I would argue that you are confusing the sensitivities of a nation with a cheap commercial enterprise... based on what happens in America to, what I believe is essentially, an Irish tradition.
I wonder if Americans actually understand the true meaning of Halloween.