Possible for some crops, but the fact remains that there *are* some which are simply too delicate to be managed with machinery.
I didn't say it was OK - I said it's a fact of life at the moment. If Mexicans didn't think this work was better than what's available to them at home, they wouldn't come here. As far as chemicals, that's a whole different topic we shouldn't get any deeper into. It's enough to say that the problem exists because people are paid to let it exist, and it would be a problem regardless of who was doing the vegetable picking.