- the uninformed, they have no idea about how the EU came about or what it does, but they're against it anyway
- the people on the receiving end of the regulations (anti-trust, advertisers, marketeers, bankers, data sellers etc). They have a very good idea about what it does, but it interferes with their preferred way of getting to more cash.
- the people that are nostalgic and that remember their country as it was 50 years ago and would like to go back there. They believe that because the EU happened to coincide with the downslide of their country that the two are related. What they usually forget is that without the EU that downslide would have been much worse.
- the people who genuinely believe that 'smaller is better' when it comes to politics and who tend to miss the wood for the trees: that in politics smaller is only better when you are very wealthy and can set your own rules. Think Switzerland. Everybody else will have a less privileged position and if they find themselves up against the giants of the world for whatever reason suddenly 'small' translates to 'weak'. In unity there is some strength so it makes sense for smaller countries to join in a larger unit, if only to curb the inevitable infighting (and the local wars that come with those).
I've yet to come across someone who actually spent some time figuring out what the EU actually does who remained against it. There is a lot of valid criticism against the EU bureaucrats: lots of them are grifters and there is quite a bit of corruption. But it is much worse in other places and on balance I'll take the grifters because I realize that politics as such is a grift of sorts, but it is inevitable, like taxes are.
Until we manage to change human nature no political system will be perfect. But given that the EU tends to stand up for the little guy and that they are powerful enough to make a difference but not so powerful enough that they are getting drunk on that power I'm ok with it.