There are absolutely no limits to what people can convince themselves of

For example, you can make yourself believe that Polish economy was in a much better shape before Poland joined the European Union than it is now. I'm not joking; if you don't believe me (and speak Polish), see here. The author of the linked post, Magda Figurska, makes altogether too many ridiculous statements to try to debunk all of them, so I'll just pick a few of the most egregious ones.

Let's start off gently. Ms. Figurska counts the fact that EU regulations forbid member states from taxing goods and services imported from other member states on a level higher than they tax their own goods and services, as a cost of joining. The thoughts that 1) taxing imports means higher prices for Polish consumers and 2) this regulation favors Polish exports in foreign markets, apparently do not cross her mind. Figurska then writes:

The sum total of our contributions to the EU budget (...) exceeds the amount of money we receive from it.

The truth, as it were, is exactly the other way around: Poland is a net beneficiary of the EU budget. Then, Figurska shifts gears and enters the Conservapedia mode: her claims become so stupid they are actually entertaining. Take this, for example:

During the so-called adjustment period, we have lost 80% of productive assets, destroyed our trade (...)

Let's take the second part of this statement first. Here's a graph illustrating the dynamics of Polish trade between 2000 and 2008 (the source of data is the CIA World Factbook):

Try as I might, I really cannot see much trade destruction going on here. Now for the first part of the statement: that during the waiting period before joining the EU we have lost "80% of productive assets." I am not sure what Figurska means by "productive assets," and she does not provide any sources of this rather staggering claim, so all I can do is speculate. At any rate, there are only two possibilities: she either means "production" or something else. If she means "production," then her statement is ridiculously wrong: the output of Polish economy has never contracted since 1990. If she means something else, then her statement is meaningless: if it is possible for a country to "lose 80% of its productive assets" but nonetheless consistently increase its production, then I submit that "productive assets" is not a terribly useful concept.

Now let me quote this sentence again, this time in its entirety:

During the so-called adjustment period, we have lost 80% of productive assets, destroyed our trade, our best businesses, steel mills, coal mines, sugar refineries, centers of scientific, technical, medical and agricultural thought.

There's really not a whole lot one can say to that, except: what world do you live in? Where on Earth did you see all those amazing things you write about that once existed but now are no more?

I'm not saying that all of the economic growth we've experienced is due to joining the EU. I think a lot of it is, but I don't know how much, exactly, and it is possible to make informed arguments to the effect that if we didn't join, we'd have grown even faster. But if you're telling me that our economy is in a catastrophically worse shape now than it has been in before 2004, you're simply ignorant.