While entertaining, and relevant, this analogy does miss a couple important pieces:

You don't give examples for the income of the drinkers. If the tenth guy makes a million dollars a month and the ninth makes a hundred dollars a month, it changes the perspective.

Also, you're ignoring the scale of costs. If the tenth guy has enough money to buy pretty much all the beer he wants, even AFTER he pays for everybody else's drinks, why is he worried about the bill?

Finally, the risk of having the tenth guy leave is always risk. But if he doesn't help pay the bill, it's the same risk. If the nine guys have to buy cheaper beer or share fewer beers, that's what they can afford. It doesn't change the core idea that the cost should be split equitably, rather than literally equally. That is, you measure the burden based on it's impact to a person, not on some abstract idea.

I let little old ladies on the bus first. Why? because it's harder for them to stand around than it is for me due to the relative ages.

If we were being equal, they'd have to wait like anybody else. I think it's better to be equitable and respect that standing around a little longer is cheap for me and expensive for them.

I suppose the argument that you shouldn't attack rich people for percentage tax breaks because you don't understand how percentages work is a good one, and like I said, I like the analogy, but I feel like it isn't accurate in some important ways.