most automatic trans fluids have a viscosity of about 0W20 which is much thinner than what is recommended. as already mentioned, the friction modifiers will cause your clutch to slip and you will soon wear it out.
a friend of mine did this for some reason a couple of years ago before a week long trip we did along the blue ridge parkway, through the smoky mountains and the dragon etc, and the heat radiating from the primary after riding all the hills with the clutch slipping was ridiculous. he ended up burning the clutch out completely and all the seals in the primary ended up leaking, i assume they were also damaged from the heat. sounds a bit much, but it's what happened, i saw it.