99% of people who believe in an oblate spherical earth don't have better reasons, they just trust some other random authority. Appeals to authority should be ignored on both sides. The fundamental reason we believe the Earth is round goes back to Eratosthenese. You can do the same calculation today as he did back then. It's based on some simple trigonometry and measuring some shadows and sticks. It's also how we actually mapped the entire globe during the age of exploration. Ever heard of a sextant or understand how it works? Most of this stuff isn't very complicated, it just seems poorly known. You shouldn't "believe" one way or the other, or base your arguments on pictures or satellites.