The only powers which national politicians have pooled, and which are therefore exercised jointly, either require co-ordination to achieve the objectives of the group or require extra safeguards before changes can be made. It can be beneficial to cede authority over some issues, to gain the advantages of free trade and mutual security.
Decisions about justice and standards are more likely to be objectively sound – to be “position-independent” in Amartya Sen’s terminology – if they are carefully negotiated on a collective basis, in contrast to decisions made by a single government with short-term political pressures upon it.
The EU has a wider perspective than national politicians and is less likely to make hasty tactical decisions. Perhaps unsurprisingly, though, given many politicians’ love of power, Sen’s argument isn’t often explained – so people tend to be unaware of the force of it and to be too trustful of national politicians to be the best guardians of their interests; as described earlier (22.214.171.124), national politicians don’t always perform well in representing their countries on a wider stage.
 Amartya Sen, in chapter 7 of his book The Idea of Justice, argued for the value of bringing additional perspectives to bear on matters of justice.