This is a naive view, and doesn’t reflect anything unique about the US justice system at all. Innocent until proven guilty is a nice ideal to aspire too, but at the end of the day, you’re dealing with the opinions of a dozen random jurors. The fact that somebody chose to charge the accused with a crime is enough to prejudice them off the bat. Defence will always carry at least some burden of proof.
Not just "a dozen random jurors", but rather "a dozen random jurors who individually usually don't want to be there and just want to go back home to eat and live their lives - and by the way, when is lunch?"
I've never been on a jury (and likely never will be - closest I got was "voir dire", and when I was questioned I inadvertently brought up the concept of a fully informed jury - and they dismissed all of us virtually then-and-there - that was over a decade ago and I have yet to be called for jury duty again), but from what I have read about other people who have, your fellow jurors, regardless of their intellect or life experience, really don't give a damn about seeking justice or truth, but rather the most expedient way to leave the whole thing behind and get back home.
Then - you get someone like me (who gets past voir dire of course) - who does want to get as close to the truth as possible by examining and questioning and discussing everything, and if there is any doubt - will not vote unanimously with everyone else (who just want to go home) - after being sent back to the juror's room a couple of times...well, most people would likely fold - because the other jurors gang up on them, scream, threaten to fight, argue, make other threats, etc - rather than actually do the job they were entrusted with - especially in a case where a person's life is at stake.
They are all quite selfish, and don't really care about the defendant, and almost actively hate a fellow juror who does care about the process, about what is at stake, and about coming to the most just conclusion (especially if that conclusion is "the law is wrong"). Jurors tend to forget that the jury is one of their most important Constitutional rights and duty as citizens in the United States; as the saying goes,
“A man's rights rest in three boxes. The ballot box, the jury box, and the cartridge box.”
Let's hope we never again need to use the last one, which is why the jury box is so important.
