Sounds like complete nonsense. I'd think you'd have to have a significantly heavy arm to cause any sort of damage, and even then you'd have to be pulling it in some fashion. When my hand is resting on the shifter, my arm is usually on the arm rest, so the only weight on the shifter is the weight of my hand. The weight of your hand, or even your arm, wouldn't be enough to overcome the mechanical forces keeping the shifter in place. That's why there's a clutch.
On the other hand (ha!), you should generally drive with both hands on the wheel. But you knew that already. :smile:
On the other hand (ha!), you should generally drive with both hands on the wheel. But you knew that already. :smile: