So you don't want what your country benefited dramatically from in the last 15 years, when Polish people moved to UK to work, sending home additional capital and reducing demographic pressure. I apologize if this sounds inflammatory, it's not meant to but: it is, objectively, a very hypocritical position.
A separate isssue is just a feasibility of Poland taking in immigrants. Before the most recent mass wave of refugees and migrants started, Poland had voluntarily taken some refugees from Syria. Since then, every last one of them left - mostly for rich Western European countries. How does the EU intend to prevent the refugees and migrants from leaving Poland?
And I find it really amusing that you talk about "united Europe" in the context of non-European immigrants. It is not okay for one country to cause a huge wave of immigration and then basically going "we can't take these people in so you have to and do it unconditionally" - which only encourages even more immigration.
Can't argue with that, but this doesn't mean EU has to take these people in, neither it gives them the right to enter the EU. Several dozen years ago these people would get their boats sunk.
I really recommend watching "With Open Gates" on Youtube and listening to what the immigrants have to say. If the picture of immigrants in the video is the reality, then the government made a very good decision by not taking these people in.