Until you have flown with someone who is a hopeless case you are not qualified to talk about it. When your sat there hopelessly low and slow on the approach, stall warner blaring and you calmy say for the umpteenth time "stick forward, apply power" and the student closes the throttle and pulls back on the controls, then you will understand. If they are not capable, they are not capable, you shouldn't keep taking their money or letting them hold onto an impossible dream, it is just wrong.
And should you finally decide your hopeless case is ready to fly solo just remember whose license the student is flying solo on, and who will be infront of the Judge at the subsequent coroners inquest should anything happen. I have seen it happen and it's not pretty or pleasant for all involved. If anyone wants to PM me feel free...