"And the only reason these people can't use an electric wheelchair is because they might collide with another object? "
Precisely - they can't control it. It's like having someone drive a car when they only have the strength and coordination to turn the wheel about 15 degrees at a time. It's only a matter of time until there's a serious accident.
Professionals will not prescribe a power wheelchair to someone who can't demonstrate the ability to control it.