For all practical purposes, we can talk about it as a law. Throw something up and it'll inevitably fall down. It's not so much that Newton's theories were wrong, but they were incomplete, and there are cases where they don't apply. So Einstein comes along with a more complete theory, which in turn is supplemented by even fancier theories, or "laws".
Sure, we can't truly know anything. But when scientist have universally agreed for centuries that Earth is a sphere, and it makes sense in every way you look at at it (weather systems, the tides, the rotation of stars, seasons, the way it'll be night here and day on the other side of the planet etc etc etc, it makes pretty good sense. Good enough for me at least, and if someone wants to challenge that, they'll have a lot of explaining to do. They can't just say "we don't know", they'll have to come up with
better explanations for the things that are perfectly explained by gravity and the planets being round.
I don't believe in the NASA conspiracy theories, and every time I take the time and effort to look into the claims, they are unvariably debunked. Often I don't even have to look for the real explanation because the guy who made the video so obviously has no idea what he's talking about. I mean stuff like "how could the flag be waving on the moon when there's no atmosphere there" when you just have to zoom in on the pictures to see that the pole has a crossbar to stretch the flag out
It strikes me as an extremely weird conspiracy, with extremely weird ways to carry out, and as usual, the supposed reasons for it are all over the place and not very convincing.
But I wouldn't want to take that whole debate here. If you believe in conspiracy theories, you believe in them and we're not going to change each other's minds.
But the thing is, so much of science today wouldn't even work if we were wrong about stuff like the shape of the Earth. Weather forecasts, for example, simply wouldn't work. They would have to be built on completely different science. That's one of the reasons a flat Earth is so easy to debunk, because if it's flat, that changes
everything. A round Earth explains millions of things, a flat Earth explains none.
Yes, if people began saying it's an illusion I might look into the arguments and the evidence. And in the case of the shape of the earth, it's very easy to find debunkings of all those claims.
Not to be rejected per se, but definitely not reliable. If billions of people can simply be fooled about the shape of the earth, for centuries, then why should I assume that anything else I've been taught is true? It may be true, it may not, and I would have no way to find out, because even the educational institutions would be in on the lies.
I'd have to see a pretty convincing reason why it would be best for whoever is really in charge, that people think the world is a sphere
Does it seem likely to you though?
Haha

Yeah, but for real I can't even imagine what the reason could be.