Well if a wheel comes off my car, or the steering fails onmy boat, or the throttle jams on my motorbike – because of my sloppy work (thatI’m legally allowed to do - with zero qualifications) – aren’t I going to crash into the same some body orsome thing?
So why are aircraft SO different? (Private operations only we're talking)
Devils advocate - the presence of a 3rd dimension in aviation almost guarantees the results will be far worse in such a situation, and gravity isn't just a good idea, its the law. In the other vehicles you are far more likely to be able to turn everything off and coast to a stop - not every time and the failures won't always be so benign, but you generally don't have to worry about a few thousand feet of drop.
Having seen what some people consider an acceptable vehicle standards, I shudder to think what would be the result if some cost conscience 'I-can-do-it-myself' yahoos without training or skills started maintaining their own aircraft. You can guarantee they won't be the ones hurt/killed when their dodgy work fails.
I won't comment on the rightness/wrongness of the legislation as I am far from qualified to do so, but I would think there ought to be at least a minimum standard for those authorised to work on aircraft. How onerous or structured that should be is up to someone who understands it in depth.