Okay, you've made the case you can sometimes jumper a dead car without starting the donor car. We get it.
What you haven't made the case for is why it doesn't help to have the donor car's engine running.
You're right, the majority of the power to turn the dead car's starter is supplied by the donor car's battery, but a modern car's electrical system can typically supply 50+ amps of additional power, significantly raising the voltage the starter motor in the dead car will see. And you're right, the alternator is not designed to handle starter motor current levels, but it is designed to put out its rated output into a load and this output will significantly reduce the battery voltage required to overcome the extra esistance in the jumper cables.
You continue to state that jumping a car from another battery is the same situation as starting a car its internal battery. It is not. A typical run from the batter to the starter motor is less than 3' while jumper cables are typically 12'+. Any you've got the resistance of the two connections. Finally, many jumper cables are smaller gauge wire than the starter motor wiring in the car. All in all, there could be 10x as much resistance in the jumper cables and connections than the internal car wiring. So just because a battery will start a car doe NOT mean that it can start another car through jumper cables. It needs all the help it can get.
And you haven't made the case that there is anything that will be harmed by having the donor car running. You realize, don't you, that after starting, the dead car will be running? So it's sensitive electrical system with all those "diodes" is hooked up the the donors car's.
There is a lot of urban legend running around about how the electrical systems on today's cars are exceeding fragile and you shouldn't hook up anything without risking damage. I am unaware of anybody who has ever had an issue with having the donor car running during a jump, assuming everything is hooked up properly.
Here are a few net references talking about proper jumping procedure. While some say you can attempt to do the start without the donor car running EVERY ONE suggests starting the donor car to assist the jumping process:
- Mark