but I think any mentally fit adult with the intention of operating an aircraft as Pilot in Command should be able to pass the 7 easy PPL exams without the need for private tuition
Most people could probably teach themselves to fly as well, as they did at the start of flight and flying. However the same arguments for not teaching yourself to fly can also be applied to ground training.
Passing the exams isnt the end of learning its just the start, after 34 years I am still learning and still keen to do so.