To disprove any theory all you need to do is show one case where the theory is wrong or doesn't work. The likelihood of anyone showing a direct causal relationship between a pulley and bearing failure is probably not going to happen. The only thing we can really do is gather enough data to support one side of the argument or the other. Unfortunately even with a lot of data, a firm conclusion seems unlikely because there are so many variables that can cause bearing failure. If the majority of the people that have UD pulleys spun bearings after 50k miles or some ceratin mileage, then it is reasonable to say that the UD pulley caused this.
I'll take my chances and let others decide for themselves.
