Why did the Elders send Ivy out? She's blind. She knows monsters are fake, but still doesn't know about the modern world. However, this doesnt explain why one of the elders didn't go instead. Its not like they would have encountered anything they didnt already know about.
Ivy had a more believable reason to go, if we consider the importance of keeping the ruse. One of the elders had already lost a son in the village to a probably-preventable death, but they still refused to go out for medicine (which motivated Lucius to try...you know the rest). So one of the elders suddenly deciding to venture out after refusing so many times would not make sense. Ivy, though, had a reputation of being brave, headstrong and manlier than some village men, and her lover was dying. For the villagers, it would be more believable that *she* would be the one to risk her life out in the woods, as she was a hot-blooded girl motivated by love.
Upon first viewing, the old-timey dialogue seems incredibly stilted and awkward, especially from Mr. Walker and some of the other elders. This makes far more sense after learning the truth- the elders are performing a re-enactment of 19th century dialogue, rather than speaking it naturally.
When Ivy learns the truth, you have to wonder what other secrets the Elders are hiding, if they are capable of making whole generations believe they're from the late 1800's with threatening monsters surrounding them. If nothing else, Ivy and Lucius may wonder this themselves.
Which is another thing- can Ivy and Lucius make themselves carry on this lie? What if they can't convince the others in their generation, like Ivy's sister Kitty, that this isn't real but they need to keep up the facade?
How could this system sustain itself even one more generation? Without the Elders acting as Those We Do Not Speak Of, people would inevitably challenge their existence and leave. If they try to recruit people from each successive generation, they rely on finding people who'd neither spill the secret nor abuse their knowledge for personal ends. At best, the Village is likely to die out, with its villagers ill-suited to modern society; at worst, it'll be worse than the world the Elders fled.
Those We Don't Speak Of attack during Kitty and Kristop's wedding. Their parents were AOK with terrorising their children and the whole village during what's meant to be the happiest day of their lives.
No, watch it again carefully: after Edward tells Ivy the story, he says "I believe one of the Elders was behind it". After we learn Noah knows too, we can infer that's who was behind the wedding attack.
Everyone in the village is white. Obviously the real reason for this is to fool the audience, since diversity and equality in an 1800s style village would instantly tip off the audience that something is off. But in universe, think about what that implies about the group that decided to start this village experiment.
It was pretty obvious from the photo that it was just a group of people who happened to all be white. Just because a small group of less than a dozen or so people doesn't happen to have a Token Minority doesn't mean they're racist.
To add to that, this started in around the 70's, possibly earlier. No matter your wishful thinking, the civil rights movement wasn't an end all be all to racism, and most of the country had racist beliefs at the time. It'd be naturally more questionable than not for a group of white, rich 70's Americans to have a minority friend.
The village is also pretty much a "gated community" mentality taken to the extreme, retreating into their own little world in fear of the Other. Even today it's practically a truism that such places will be overwhelmingly white.