That's like saying one would increase resistance to pollution by ingesting it.
I know that pesticides are water proof and even using soap it's difficult if not nigh impossible to get it off, so what's the point? All you're really washing off are the bacterias, germs, and anything else that could be on it like poo. The thing most people are worried the most about you can't clean off anyways.
Some of the most popular things out there like any kind of berry, apples, lettuces, even if washed with SOAP they have very high levels of pesticides.
So to be honest, yeah... all you're doing is wasting time. It's like a placebo. The stuff you're washing off is largely bacterias and despite most people's hypersterile beliefs, that stuff is actually beneficial to your immune system. If you built up resistance to it your entire life compared to never being exposed to it you'd have a much stronger immune system.
The only reason the FDA suggests washing them is to prevent food poisoning, e.g. e coli. And for that, to be honest, you'd be better off using vinegar or hydrogen peroxide. Water's not gonna do much and soap has too many of its own nasty chemicals. Personally, I don't really like the idea of cleaning my food with vinegar or hydrogen peroxide and I know the adverse won't do fuck all.