If that's not enough reason: most (if not all) fix a flat's use Butane
as a propelant and inflator. It's not as stable as air and is flamable.
Also, if you don't get the tire spinning immediately and keep it
spinning for a while it won't be anywhere close to in balance. It's
better than having a flat, but it is a temporary fix at best. Also, if
you use one, warn the tire person when you get it changed or fixed.
Sometimes they smoke...

John