> The other side of that coin is that the wealthy consume less of a percentage of their income and invest a greater percentage.
Yes, which is why I'm not advocating an oppressive level of taxation. There is a huge range of tax levels which qualify as progressive. Your argument sounds like advocacy for trickle-down economics, which have not been very successful historically, especially in the 2000s, where income disparity has continued to increase.
And yes, poorer people invest much less, which is why it's in the interest of society to increase the possibility of the least wealthy to be in a situation where they have at least a low level of disposable income. That has historically meant a bare minimum of income redistribution, some forms which have worked, others which have failed spectacularly. I have yet to see that a difference of, say, 10% of the wealth of a multimillionaire drastically affects their investment habits, but such a difference for a lower-class consumer has immediate, measurable effects on consumption habits.
I make the case only for those with seven figures of income and above; I believe there is an important case for those with $1-10 million/year to heave access to good investment options.
> You honestly don't see that there's very real theoretical and real world downsides to involuntary redistribution?
Yes, but the arguments that advocate against wealth redistribution are, in practice, extremely poor and have little, if any, empirical support, while the effects of public education, public transportation, and social safety nets are evident and are the cornerstone necessary to support modern first-world economies. They are responsible for the knowledge economy by lowering the bar for higher education, greater availability of workers by increasing mobility and lowering the cost of living, and having more productive hours by maintaining the general health of the populace which, even in the absence of mass universal health care like in the US, still has public interests in the form of various regulatory agencies that control pollution emissions, drug testing, and general public health policy. The nitpickings of the particular failures of such agencies are interesting but contribute little to the debate, as the fundamental point is that by and far they serve and achieve their purpose, and when compared to countries that have little legal and enforcement options on those issues their success is evident.
The question is not IF there should be redistribution, but how much. My personal stance based on empirical evidence is less than Scandinavian countries, more than the US. The ethical dilemmas of involuntary redistribution are the same as those for taxation, conscription, and other more mainstream issues regarding personal liberties and positive and negative rights and obligations. I don't consider this one to be very debatable in comparison to more relevant topics of this day and age.