P: Vote for me! Free movement of labour is great.
C: Why? Then I will face competition from people who are willing to work for very low wages, and so will my kids.
P: Yea, but then you can move to France with your family!
C: Ok but I don't want to move to France. I don't speak the language. My friends and family are here. My kids go to school here. And why would wages be better in France, anyway? I'll face the same competition there.
Can you see why this may not be very convincing? On the other hand, imagine a conversation with the owner of the shop:
P: Vote for me! Free movement of labour is great.
O: Indeed, I'll be able to hire cheaper workers.
I think the better counter argument is brain drain, it's certainly not advantageous for a country if many of its most skilled citizens leave. Personally, I think it's just wrong to build berries of any sort for your citizens to leave the country.
There is plenty of logic of being sceptical when Danes aren't getting jobs at their normal rates because they are being underbid by eastern european workers taking work in their countries while Danes moving to eastern europe won't get the same benefit.
The major problem with the EU is that the expansion towards underdeveloped countries happened too fast.
It's one things when countries are fairly equal, but the difference between the north and the south and the east and the west is quite staggering.
This is all part of why people are skeptical. Both because it's logical to be so and because they are being emotionally afraid about their future.