Why are trading blocs such as EU are considered as a major threat to the member of states sovereignty?

The aim of trading bloc is to encourage the free movement of goods and people. It is true and evident that trading bloc persistently integrating more area to its jurisdiction such as EU today. I think that further integration would lead to further stablity, prosperity and equality within the member states in the tradic bloc. Look at the economic growth in Ireland today. Before they joined EU, their GDP per Capita is extremely low. But, after they had joined the EU their economic growth has consistently increased very rapidly and thus eventually qualifying as an MEDC country. My point is that, why there are so many people who viewed EU and other trading bloc as a threat to their sovereignty while they could simultenously uphold prosperity and equality among the member states? Why there are so many people who anxious and displease with the integration and bureaucratic movement when their implication is actually a source and influence to the economic growth of every member states?