Indeed, the "root argument" in favor of taxation is fundamentally all about "having other people pay more so that I pay less". That being the case, why did you start out by saying that "investments should have much higher tax rates", only to contradict yourself later?
I could support the fist line by saying investments are taxed at below average rates including loans (bonds) which are not double taxed. And a flat tax without any form of tax breaks is the only fair solution.
But, again not trying to support a position just disappointed with the way taxes are discussed. Arguably all people deserve a tax break, but the only way to do that is reduce spending.
In other words, if you just hold some money for a few years and it doesn't lose value (interest rate equals inflation), you _already_ owe tax on it. That's just broken.
If we did capital gains in inflation-adjusted dollars, the situation would be somewhat different.
I have yet to see good solutions for this problem.
Really, you can try to justify any tax policy by reframing the question, but the root argument breaks down to having other people pay more so I pay less which is never really justified.