BINGO! Without illegals picking the lettuce, we always hear the threat of prices like $10-a-head, as if we HAD to buy it. The first time lettuce got too expensive, it would rot in the fields. The farmers would scream bloody murder. The following year some smart guys at an agricultural college would invent a lettuce-picking machine and the prices would go back to normal.
A side effect of slavery, whether in ancient times or in the pre-1861 U.S., was its smothering effect on innovation and invention. If you can always have cheap/slave labor, why invent labor-saving machinery?
You have correctly identified the exploitation of illegals as slavery. All too many of the open borders crowd fail to see the immorality of the situation, not to mention the cultural and economic costs which are hidden from us.
Perhaps that lettuce will cost slighly more. Other costs which are lower will compensate. I trust the free market to handle it.
Actually, the labor cost of a head of lettuce is a small fraction of it's retail price. It's been shown that doubling farmworker wages would add about 15 cents to the price of a head of lettuce. The simple reason that agribusiness uses squat labor is due to the commodity nature of the business and the fact that since the labor is available, why buy machines? The machines you allege to be invented have already been invented, as far back as the '50s: tomato and lettuce pickers . But further refinement of them was quashed at U. of California in the early '70's at the insistence of the UFW to Jerry Brown and the CA Dems (i.e., the program was de-funded). Why? Because the UFW knew even then that farm work in California is nothing more than a make work program for Mexico.
And that's the short answer to everything: all of this is happening because Mexico has a stratospheric birth rate, with no economy to employ them. And never will, for a variety of reasons. But apparently no one in the respective governments wants rebellion in Mexico, which is exactly what SHOULD happen. So Mexico exports its population (it's the only thing they actually know how to make), and the U.S. accepts it, in the interests of political stability...in Mexico.
And guess which people get stuck with the ultimate costs.