I'm not sure what arguments there are against taxing the rich. The most common I hear are:
1: Offshoring (well, then we need all countries to work together to root out tax havens)
2: The rick are entitled to their money (that's true to a point - I mean, if I found a business, then I'm entitled to take more from that business than others I employ - but we have progressive taxes for a reason. You don't need billions of dollars each year to live)
3: Billionaires are a source of philanthropy (again, also true, but the question is, who's better at raising the standard of human life - philanthropists, or governments? I think that's a question worthy of debate, but there's a saying that "charity is due to a failure of government." So even if Bill Gates for instance is a philanthropist I admire, there's still an argument to be made that his money would be better served with government)
4: Trickle down economics (okay, so having looked at the data, if we take the neoliberal era as beginning from the 1970s, I will concede that this period does mark the greatest reduction in poverty the world has seen. However, two problems. One, a lot of this poverty reduction comes from China, and whatever China is, it certainly isn't neoliberal. Second, in terms of growth, most of it is still captured by upper economic percentiles. I'm skeptical about degrowth for a number of reasons, but growth for the sake of growth isn't progress either.)
So, yeah. Tax the rich. Tax them, so we don't eat them.