Earlier quoted context omitted.
This seems like the obvious solution, make up the difference by taxing dividends and capital gains as if they were income. I'm pretty sure this is where we will end up anyway, there seems to be a race to the bottom. It's much harder to move your family offshore to avoid tax than it is to move your profits offshore.
This is how capital gains and dividends used to be taxed... The capital gains preference is a relatively recent development in the tax world.
For example, if you bought a lump of silver thirty years ago and sell it today, the nominal price is higher, but that's basically just a result of inflation. Shouldn't we be taxing the real gain and not the inflation? But in that case maybe instead of a lower capital gains rate we should only adjust the gains for inflation and then apply the normal rate.
Then you have the double taxation argument, but in that case you should either just get rid of the double taxation or dividends should be treated the same way.
And there are several others, but what they all amount to is that the lower rate is a bad hack and we would be better off in each case to account for the thing that needs adjusting directly instead.