I don't know if I'd quite agree Foxy.. because if someon is, as you said, frightened due to understeering (I assume that just means you are going into a turn and you can't turn the car as it is plowing, so you might hit something), that simply means he/she is going too fast (for the car / chassis / suspension / tires).. you back off the throttle and the line tightens.. it is not the fastest way around the turn / the track, but you don't swap end.. and spinning out means you have pretty much lost control and you most likely only can put both feet in (clutch / brake) and lock it up and hope you don't hit anything..
An inherently oversteering car is less confidence inspiring, because it takes quite a bit of commitment (to plant the rear, you need to be on the throttle, BUT, you might run out of room when tracking out (after the apex), if your line is not perfect). I am certainly not saying that it is ''bad'' (it is faster around the turn / track), but just saying that for most people, it is more dangerous as having the tail stepping out / spin usually scare most drivers.
You are talking about driver levels -> a pro driver probably don't get frightened for either anyway as they understand how chassis react to their inputs. If the car understeers, they will know how to deal with it. If the car oversteers, they also know how to deal with it. And most likely, they will adjust the setup to suit their driving style once they found out the current setup of the car.
I think we need to qualify driver levels. If my wife for example, had a high power rear wheel drive, she'd probably crash it if she tried to drive it fast. So in that sense, yes, understeer is 'safer'. However, for those who can drive well, understeer is very frightening, for the simple reason that there isn't much you can do about it. All you can do is stab the brake and hope the forward weight shift makes the front tires grip again. At least with oversteer, there are several subtle ways to respond to it. I've never ended up facing the wrong way in the S. It's nearly killed me a few times, but I never lost control of a spin.