Does your second point suggest that we should avoid eating beef?
Remember that all risks are relative. Just like radiation, there's likely to be a background level of prions in the soil that you can't avoid even if you only eat vegetables. The question is how much prion exposure you can tolerate without having noticeable symptoms within your lifetime.
I eat meat occasionally as well. I tried going vegetarian for a six months, but I lost an unhealthy amount of weight (my BMI dropped from 19.2 to 17.8) and I think the health risk from malnutrition, as you also mention having struggled with, is much more severe than that of prion disease