I agree and I took a similar path to the the same conclusion. Perhaps in a very dusty/sandy environment I would use one, but the place where you really notice crap on the lens is the eyepiece lens. A tiny drop of water on there and you'll be going, "WTF is that black thing, am I getting floaters in my eye?? And why aren't the floaters floating???"@Convex I like your arguments for using filters, very cogent and detailed. Here is my contrarian view on the subject.
For cameras: I used to religiously buy UV filters for all my lenses and leave them on. Over the decades, I noticed that sometimes led to artifacts in the pictures and some softening of the image under certain conditions. About 10-15 years ago, I removed all these filters and never looked back. I do use a sunshade all the time, and I am totally cognizant of possible issues with them under certain conditions and deal with that appropriately.
For riflescopes: I played with various shades of yellow filters on riflescopes to see if I could enhance mirage conditions, reduce haze, and whatnot. I have 3 different yellows in 62mm in my rifle bag if ever I want to try again. I am not in favor of adding a filter to a riflescope for 2 reasons.
1- A photo filter is not built to withstand the G-forces of rifle. These filters are made for camera lenses which (usually) do not get banged around anywhere near what is experienced by a riflescope. If the filter breaks, it's liable to scratch the lens underneath, or worse if you actually have a filter on the eyepiece. To protect the objective lens, I always have a sunshade installed. It keeps fingers away from the lens and anything this is able to get to the lens with the sunshade on will not be stopped by a filter.
2- I paid a lot of money for my riflescopes and I want to have the best IQ I can get from them; adding one or two more lenses is not conducive to increased IQ; in fact, I think it's counterproductive.
This is all very subjective, and it's always interesting to see the arguments for and against the use of UV filters on photography discussion boards. It appears most pros eschew their use in favor of the best IQ from their lenses. But I'm sure other pros or advanced amateurs can make a good case for their use. As I said, subjective. But one thing that's never mentioned in these discussions is the effect of rifle recoil, which I think makes a huge difference.
tl;dr: I don't use filters on riflescopes, and I recommend against it for safety reasons.