What do you mean? Eloquence and persuasive methods have existed at least since Antiquity (just look at the records of Plato in Greece). What it takes to believe any kind of BS is just the absence of critical thinking. This is the real root cause.

I really doubt that pure eloquence can compete with the visual smorgasbord that modern marketers can create, all learned after spending billions on mass market advertising over decades.

Plato couldn't laser-target his message to 5,000 different segments carefully curated with an extensive re-marketing campaign.

They never accounted for flat earthers, but no amount persuasion or marketing is going to change my mind. Stupid is as stupid does.

Oh, I see. This time is different. Human nature has fundamentally changed.

Anyways, I always read the flat earth argument as an exercise in rhetoric. From that perspective the outrage over it speaks volumes.

They also didn't account for universal suffrage so didn't have to worry about the idiots who would fall for these.

Landowners in general would be a good place to start, people who are smart enough to contribute to society and have a vested interest in the country succeeding.

Every citizen has an interest in the country succeeding. I rent because I live in a densely populated area with high land prices. Does this mean I'm not contributing to society or would be ok if the country failed?

That's why they designed it based on principles.