Some of the comments on this thread turn my stomach.
If someone is in a wheelchair there is normally a pretty good reason as to why, normally this is because they are not fully in control of their body and this includes control over some of their most basic functions, probably the reason for the smell.
Cabin crew are supposed to be trained to deal with less able bodied passengers, this is part of your job, you don't get to choose your PAX. All credit to the Captain for declining to offload the unfortunate individual.
Back to the training centre for you, tuismile, and I hope not to meet you on my travels