While I agree with much of your post, current taxes on income (featuring reduced taxes on capital income, exclusion of most income from gifts/inheritances, and supplemental taxes on labor income [“payroll tax”]) absolutely disincentivize working for income if you have choices of how to get income. Now, lots of people don't have choices and are stuck with work, but that doesn't mean there is no disincentive effect.
(Of course, “treat income as income” makes this much fairer than the status quo, much less the laughably misnamed “FairTax”.)