and with many quite extreme theories like the flat earth theory

Being good at theorising anything is a science and should be approached with a scientific perspective.

And this is why "conspiracy theorists" sound like raving lunatics.

Let us get rid of "flat earth theory" and call it what it really is, "ball earth disproof"
But almost no one can think scientifically, so a disproof is a nothing.
You are trying to get a normie to let go of a 'fully formed, often reinforced, pounded into their brain, theory of how a thing works' with ... nothing.

Scientifically speaking, the ball earth model has been disproven and debunked so many times, that every scientists should have thrown it out already.

Disproof: You can see things past the curvature of the earth, thus the ball earth model is wrong.
Disproof: There is more land mass south of the equator than the ball earth allows for, thus the ball earth model is wrong.
Evidence: Almost all images of earth from space are composite images. i.e photoshopped.
Evidence: Airplane routes do not conform to a sphere, the conform to a flat earth map.

So, what does this say about your two above statements?
If you actively believe in the scientific method, than the ball earth model has been disproven.
And if so, then why do you call it an 'extreme theory' ?

Thus the person that is being called a 'conspiracy theorist' is probably in their correct mind, and having an appropriate emotional reaction to the person listening saying "i will believe in what my teachers taught me despite all facts to the contrary"