An interesting post Mazzy, but you are missing one vital point, that any job eventually becomes that. A job.
I love flying, I have spent 10's of thousands on it and I am very lucky to be able to earn a living from flying aircraft, but I never lose sight of the fact that it is a job.
Sometimes it is awful, sometimes it is the best thing in the world, but flying for a living is a whole heap different from being a PPL.
An FI doesn't get the choice as to who they fly with, where they fly or when (obviously wx is a factor) and you are constantly at work in the cockpit, or on the ground.
Many people make that mistake and try to equate PPL flying with teaching. The two things are totally different, yes you are up in the air, but that is about the only similarity.
It's about as different as going for blast across a wonderful mountain pass on a beautiful day in your new car compared to slogging up the motorway driving a lorry.