It's dumb, like a lot of things in the prequels. Actually, as of the prequels, I've found the Jedi to be not just dumb but actively horrible and evil -- thuggish killers whose only redeeming feature is that they're not quite as bad as the Sith they want to exterminate.
Ugh. I agree that the Jedi were not well thought out in the prequels and it brought up a lot of odd questions about how their system actually worked, but the idea that the Jedi were actively evil is as tedious as the idea that the Empire were really just misunderstood "good guys".
Both the Jedi and the Empire can be the baddies with the Sith aligning themselves with the Empire to get help in fighting those who seek to exterminate them.
The Jedi's moral code doesn't even include opposing slavery. If Anakin was just a child slave and didn't have force powers, they wouldn't have lifted a finger to help him -- as indeed they did nothing for his mother. When given the "gift" of thousands of people with abusive childhoods, they decide "Hey, let's take these kids and use them as shock troops." There is no effort to give them rights or help them recover from their abusive childhoods. They don't just tolerate slavery -- they actively participate in it.
More broadly, they act to violently enforce the law, with no question of whether the law is wrong or right. The only exception to this, it seems, is if the law is by a Sith -- in which case they try to kill them. As Palpatine rose to power, they had some thought that it was a bad direction -- but they took no action against him. It wasn't until they learned he was a Sith that they acted. If he had just been a non-Sith bad guy, it's unclear when if ever they would have opposed his rule. Maybe they would have, but given that they took no action even to oppose slavery, he'd have to go very far for them to actively oppose him. They took wholeheartedly to owning a slave army and violently suppressing the Separatists, after all.
As portrayed, the Separatists are evil -- but the Jedi attack them not because they're evil, but because they are Separatists. They don't take any action - even mild action - to oppose other evil regimes like the Hutts.