Going skydiving, with a class, with a parachute, with a backup, is still dangerous.

Climbing a mountain with good equipment and a buddy is still dangerous.

Being "properly prepared" is only relevant inside a context. You can't look at just preparation when deciding if something is too dangerous. The actual risk numbers are the important thing here.

If I'm driving 100 miles, and I do something sloppy that doubles my risk of dying in a car crash, the actual danger I face is less than the danger of skydiving just once with perfect prep. If it's also a special occasion where I'm going to get a huge amount of enjoyment out of it... the risk seems okay.

Even if we're focused just on car safety, we should be far more upset when someone buys a car without top-tier safety ratings than about some one-off trip like this.

Being able to point at some specific danger, like a battery on the floor, is just bikeshedding. What matters is the risk per day/month/year, and most of that risk is invisible.