I am sure most with stable jobs and proper contracts within the EU fare well. However, the no borders migratory work force tends to be made up of the poor who will take any work for any wags, forcing wages down, not up, and making it bad for the indigenous workforce who find themselves stuck at the bottom and at the mercy of employers who want to pay them peanuts. Some people will accept peanuts. Unions have existed to ensure workers, mostly with no voice of their own, get a fair deal, and rightly so.
The late Union Leader Bob Crowe was anti-EU for all the right reasons.