Hey, you might have all seen this extensive bitch-fest about how Midi-chlorians were indicative of everything wrong with the Star Wars Prequels in one of Rorie's video features. Since it was so long and everything, I figured I should add it to my blog. I apologize in advance... all over again.
Midi-chlorians were pretty symbolic of the main problems with the Prequel Trilogy. Lucas explained things people didn't need or want explained (The Force, Boba Fett, C3PO), and almost all of the explanations and background information he did come up with destroyed a lot of what fans had come to assume and love about his characters: The Emperor didn't look like that because the Dark Side physically corrupted him, he actually just shot himself with lightning; Yoda being a great warrior through his power in the Force wasn't because he had mental mastery over objects that emphasized that size and strength were unimportant, he was actually just really spry and could flip around and shit with a tiny lightsaber (which he arguably did with the Force, but it still ruins the concept); Obi-Wan didn't hide Luke on Tatooine because it was a backwater planet that nobody of any importance really knew or cared about, he did it because that's where Anakin was born (y'know, the guy he was trying to hide Luke from?).
Star Wars was about a galaxy far, far, away. The possibilities for the franchise were limitless, but every choice that George Lucas made in the Prequels made the series seem so small, so coincidental, so... self-centered. It wasn't good enough that Obi-Wan and Anakin were friends under Yoda's tutelage and the Emperor rose to power during the Prequel timeline. That wasn't enough in his eyes to cement the movies as "Star Wars". Instead, he found ways to work around what little we were told about the events prior to the Original Trilogy (like Obi-Wan not recalling owning any droids-despite 3 adventures with those specific droids and having an Astromech of his own on his starfighter). No, instead, we needed to see that Anakin built C3PO, a protocol droid, for his mother, on a planet that in A New Hope it's made apparent that protocol droids are unnecessary. We needed to see that a smuggler Wookie named Chewbacca was actually a respected warrior that specifically protected Yoda during a battle right before his exile. We needed Boba Fett's history to specifically tie into the adventures of Obi-Wan and Anakin Skywalker. It was manipulative and cheap that he was constantly tying classic characters into a storyline that they obviously didn't belong in. Instead of developing his new characters, most of whom were pale imitations of their predecessors, we were forced to sit and wait for the next ham-fisted cameo from a beloved character that destroyed what we liked about them in the first place. I'm amazed he showed enough restraint to not have a little Han Solo save Chewbacca's life in Revenge of the Sith to explain the "life-debt" that Han mentions in the Original Trilogy!
Sometimes, what's left unsaid is what makes a character or a movie as memorable as it is, and the Prequel Trilogy is the perfect example of this. Keyser Soze, The Joker, The Man with No Name: these characters are loved specifically because we can't define them. The mystery is what intrigues us, it allows us to fill in the gaps the way we want them filled in. After twenty years of filling in the gaps ourselves, nothing Lucas could come up with could compete with our own imaginations, and some of his answers directly contradicted what many of us had come to accept as the best possible scenario (oh, Old Ben's ratty robes weren't because he was a pretending to be a desert hermit to avoid Imperial attention? He was dressed in ceremonial Jedi Robes despite the standing order from the Emperor to hunt down and kill all Jedi?). Thanks for nothing, Georgey.
Specifically returning to your main question, though, giving a scientific explanation to something that was previously viewed as mystical ruins the "magic" of that force; it takes away the dreams of every little kid that went to see Star Wars and secretly hoped that someday they could be a Jedi like Luke Skywalker. Sorry kids, if you don't have these little microbes in your blood, it ain't happening. It also needlessly convolutes the fact that the general populace of the Original Trilogy now view The Force (which was well-known and commonplace only 20 years earlier) as a hokey ancient religion full of mumbo-jumbo. Nobody wrote down what happened? All of the science books in the Star Wars universe were destroyed and everyone's memories erased? That's quite the iron grip that the Emperor has on basic and common information throughout an entire galaxy of planets... I always thought that The Force was just like an extra sense, an extra dimension to that universe that could be observed and manipulated by those who were trained in the arts and that with enough work and concentration in these lost methods, anyone could potentially become a master of The Force (though some would be more naturally inclined, like with sports). Instead, it was a bunch of little bugs.
Sorry, nerd rant over.