Who gets to decide how much is too much? ... people in those countries getting rid of their corrupt politicians and levying taxes on their own wealthy.
Something tells me you answered your own question just there. And if it is 'the people in those countries' deciding when too much is too much, then the GP poster commenting he feels Gates has too much is certainly within his rights to say.
Saying that the problem isn't that some people are too rich, it's that some are too poor is trying to make excuses why being overly successful (in some cases, abusively successful) is desirable and 'them good for nuthin' lazy poor folk' are in the wrong for not being successful enough. The whole game is set up so that a few accumulate a lot that could otherwise be feeding the many. The phrase 'you have to have money to make money' didn't come about because it's a cute saying. I can't imagine that anyone that's rich now continued to slog away on the assembly line until they were rich. At some point they stopped doing manual labor and let their funds work for them through investments. Even still, SOMEONE needs to slog away on that assembly line, don't they? Why can't they be paid commiserate with the total value their work brings in, just like those awesome investors that ponied up a little dough but didn't otherwise put forth ANY effort for their return? It'd certainly keep them unsuccessful poor from being so poor, wouldn't it?
The simple fact is that people are greedy assholes no matter which end of the 'rich' spectrum you're on. It's just that those that have (money, skills, power), they get to flex their greed more strongly than the rest. If everyone played fair on their own, sought balance instead of their own aggrandizement, we wouldn't feel the need to put in such silly things like regulations and limits and 'how much is too rich' and such because you just wouldn't have that problem anymore.