There is hard evidence these checks prevent crime (i.e. smuggling and human trafficking), as well as evasion of judicial measures. So, since these checks will not just go away in the foreseeable future, he needs to provide a better alternative.

Edit: I don’t really get Denmark and Benelux tho. I doubt there is that much going on via these borders, but maybe I’m mistaken? I can see smuggling over their ports could be a problem, but that could be resolved by tightening security there instead of at the borders.