Everyone hates on midichlorians. I don't understand what the big deal is. We knew people were force-sensitive or not, and we knew it was hereditary. So he threw in a concept about what it is that allows SOME people to feel the force and others not. "Testing positive for Jedi"? That concept was around from Ep IV on, it just wasn't formalized as a blood screening test. The Jedi still didn't rely on the test to look at aptitude, and there is no evidence that they tested every baby to find force-sensitives. They sense a child is strong in the force, they may or may not do the test. It was a plot point to demonstrate Anakin's potential to be the most powerful Jedi ever. That is all.
(My only problem with the concept is that midichlorians, as described, sound like they are based on mitochondria... which are passed through maternal lines rather than paternal lines. So Padme was really the force-sensitive one... only not... Don't do science-ish stuff if you are gonna mess it up.)
The deal is that if you formalize the Force to the point of it being a chemical reaction in your blood, it rips the entire spiritual framework of the movies. Every wise thing Yoda tells Luke on Dagobah ceases to be wise and becomes deliberate misdirection. The Jedi teachings become smoke and mirrors that conceal simple chemical and biological processes. The Light and Dark side cease to be about morality and choice, they become different and equally valid schools of applied science. The Force literally becomes a hokey religion of parlor tricks like Han Solo said.
I'll bet there's some interesting connections to the changing perspectives on science and religion that were occurring in the late 20th century. I'm sure there's a philosophy paper on that somewhere