That first paper is not showing a positive long-term effect for healthy men, it’s showing some cognitive return to normal for people who have a cognitive
impairment, possibly associated with their ED. It’s wrong to jump to the unsupported conclusion that it might help old people in general. On top of that, 17% of the very small sample had to bail out of the study due to excessive side-effects.
It’s not useful to say other things have side effects without actually comparing magnitudes or dosage. Everything can kill you if you ingest too much. The call the FDA made is about the relative severity and danger level, and they allow lots of things OTC that have side effects. Why do you not believe that Viagra is more dangerous than Aspirin, why are you armchair second guessing that call? I’m pretty sure Aspirin is far safer than Viagra when used as directed, and that people sometimes take a lot of it because it’s a pain killer and believed to be quite safe. Two thirds of Aspirin deaths are attributed to taking high doses, where Viagra is rarely if ever taken with higher than prescribed dose because everyone knows that’s pretty dangerous.