No, it wouldn't be great at all. Even in the unlikely event of the fatty actually being disabled, there'd be no need to assault the wheelchair user. Ignorance is not a disability.
As a disabled man (crutches now, wheelchair in the past), I abhor this "let's use the disabled loo/parking space etc" attitude by the lazy, selfish, ignorant cwnts.
Disabled people need the extra space in car parks, for example, as they may need room to transfer into a wheelchair, or in my case, I can't bend my knees sufficiently to exit a car in a 'normal' space.