Poland will not accept refugees, they pose a threat to the country’s security

So now we have a number of countries that, like the UK, want to have the benefits of being in the EU, but none of the responsibilities. If Poland wanted its "sovereignty" why did it join the EU? Now that it's joined the EU, why does it refuse to play by the rules?

Isn't it too late now to think about sovereignty, especially for the last two batches of countries to join, long after the establishment of the current trend for "ever closer union"?