To be extremely reductive, allowing false beliefs into one's web of beliefs corrupts it. This typically gives rise to a multitude of other false beliefs. Flat earthers almost never only believe one obviously false conspiracy theory. They become epistemically susceptible, and worse still, they tend to spread these awful ways of thinking with great zeal.
In the more general case, I recommend you learn about the ethics of belief. The Standford Encyclopedia of Philosophy page on the topic is a good starting point: https://plato.stanford.edu/entries/ethics-belief/
Maybe someone can come along and answer your question in a more succinct yet equally (or ideally more) convincing way. This request that you commit several hours to educating yourself is the best I can do at this time.
How do you inform a voter on the implications of say, tax policy, and expect them to make a rational decision if they can't even comprehend that the earth is proven to not be flat? Ignorance and its tolerance hurts everyone in a democracy.
It's not that curious, it's pretty clearly self describing actually.
And what's wrong with arguments against democracy? We are in a thread explicitly discussing questioning anything and everything and talking about the virtues of being averse to dogma. What if democracy is not as good as it gets? What if there's an alternative that is not authoritarianism?
For flat earthers in particular this video sheds some light on why their way of thinking is harmful: https://www.youtube.com/watch?v=JTfhYyTuT44
To be extremely reductive, allowing false beliefs into one's web of beliefs corrupts it. This typically gives rise to a multitude of other false beliefs. Flat earthers almost never only believe one obviously false conspiracy theory. They become epistemically susceptible, and worse still, they tend to spread these awful ways of thinking with great zeal.
In the more general case, I recommend you learn about the ethics of belief. The Standford Encyclopedia of Philosophy page on the topic is a good starting point: https://plato.stanford.edu/entries/ethics-belief/
Maybe someone can come along and answer your question in a more succinct yet equally (or ideally more) convincing way. This request that you commit several hours to educating yourself is the best I can do at this time.