Learn English – What’s the meaning of “gas” here

Lincoln is saying that there is much controversy about whether runaways from "service or labor" should be given up to their former masters on demand, rather than being protected from going back. The structure is:

There is much controversy about the [handing over/sending back] of [fugitives from service or labor] when their masters demand their return.

So here deliver [something] up means to surrender it back.

It means stealing the rims from all the cars in a Chevy dealer's lot. "They" means unknown criminals, not necessarily Mexican, who are stealing the rims because of the demand from the Mexicans.