Hooray! Finally we’ve got some honest talk about the idea of having local law enforcement go after illegal immigrants. Bottomline, cops do not want people to scatter every time a cruiser rolls down Central Ave, for example. There would be substantial costs in time and money and, likely, overall police effectiveness in terms of solving crimes were the locals to become de facto immigration agents.
This does not automatically render a Myrickian drafting of local law enforcement into immigration and border control a non-starter, but the test of any policy is how it would work in the real world. Better to get the facts on the table sooner rather than later.