The EU obviously isn’t inherently good for worker’s rights, but it has ended up at a decent position with regards to them, so I can see why people stick to the “it’s a good thing!” position.
Worked a while back on some EU stuff to do with the Renewable Energy Directive. One of the things I learnt was that, partly because of the way the EU is set up, with the Parliament, Commission and the Presidency all putting forward different versions of text etc on directives, there’s a sort of internal competition to be seen to be the most progressive / responsive etc. And because the Parliament is lower profile in the public eye, MEPs are more inclined to push things that will them in the public eye. As a result green interests had a lot of influence on the renewables stuff that they probably wouldn’t have had in a UK scenario.