If 30fps were fine
If Carl Benz said "Horse carriages are fine. They work!" we wouldn't have cars today.
- smartphones would run at 30fps instead of 60 or 120
- game developers wouldn't even try to push for 60 or 120fps
- there wouldn't be people saying 30fps are not fine in the first place.
It's kind of a tricky situation, as some games might benefit a lower FPS for aesthetic reasons while other studios push to top out FPS for maximum performance out of a console and TV setup.
Going back to FPS aesthetics. For example, if you look at film, FPS is set at the standard of 24 frames.