The problem is that humans are bad at sitting there paying attention while they're not actively engaged, which is what's required to use FSD safely. Also, FSD has essentially no benefits if you use it safely. If you listen to someone talk about what they want FSD for, they'll probably tell you they want to be paying attention to something other than driving or that they want to sit in a more comfortable position where their feet aren't on the pedals and/or their hands aren't on the steering wheel.

The current Tesla FSD beta has no purpose other than as a tech demo, but people absolutely treat it as if it's ready to be your chauffeur while you take a nap in the back seat.