> a single engineer personally adding a jet engine to his car while seemingly being very in touch with the dangers of operating it

What if a non-engineer who doesn’t understand the dangers makes this type of modification? This is is why it needs to be illegal. Just because someone straps a jet engine to their car it doesn’t mean they know what they’re doing, and _that_ is the risk, and why pretty much all laws exist in the first place. Many people could drive safely without speed limits, but we have speed limits to cater for people who can’t. My point is that if this type of modification truly is legal in America, that’s scary, and Australia got the laws right. A jet-powered car is not inherently safer in the US than Australia.