5) The difference is that if you're doing it for profit, there are laws that govern that activities and you must follow them. It is really simple.
To me having insurance valid for commercial use seems reasonable, but you don't need special licenses or laws to enforce that. Just have a law that says "you must have insurance valid for the kind of driving you do" (which I suspect Germany already has).
The basic point being made here is there is no technical or medical reason why the amount of money being charged suddenly makes driving fundamentally different. You're driving the same car on the same roads with the same driver. So why have governments made it so complicated?
This is everything the court asked for: Appropriate insurance and regular checkups (yearly instead of biyearly).
Licenses provide the proper checks and balances proving that the driver has complied with their legal requirements. The license is typically shown somewhere in the taxi, so the fare can see that they are covered if anything bad were to happen.
That's of course assuming the fare knows about this, which for foreigners isn't always the case.
And that jurisdictional difference exists because it is profitable for cities. The consumer does not benefit at all.