2) “The horizon always rises to the eye level of the observer as altitude is gained, so you never have to look down to see it. If Earth were in fact a globe, no matter how large, as you ascended the horizon would stay fixed and the observer / camera would have to tilt looking down further and further to see it.”
This is nonsense. It just isn’t true.
It depends how high you go. Plenty of people have gone high enough to see it, but flat earthers evade that by claiming that “they’re all in on the conspiracy, and their photos are fakes”.
As Daimonie shows:
“The horizon always rises? No, it doesn't. What do you think the horizon is, some mythical creature? Let's show what it is. Suppose for a moment that you're shining a laser while standing on a huge sphere. You start by pointing it upward, then move it downward towards your feet. The Horizon will be that point where the laser first hits the sphere. Yes, again, it is that simple. A slightly more complicated story allows us to calculate. I took it off Wikipedia/Horizon, and it includes the calculation.”
Again, see this video for more details