Instead he should be pushing the argument "Why the hell should I have to pay for all these government just because I'm more productive than other people? If I use $10,000 a year worth of government services why am I paying $200,000 for it while some other guy using $10,000 a year of government services pays nothing? Why can't the burden be spread more equally among all those who use government services instead of lumped almost entirely on the top 10%?"
That's the argument he should be pushing. Of course there are possible responses to that, but it's a better starting point for debate than "I only make $500K a year, you should tax the real rich, who are making $800K a year!"