This seems like a common point in this thread with which I respectfully disagree.
While I'm sure we all support the notion that there is social good in reducing income inequality in the U.S. and improving quality of life for all, consumers in lower tax brackets will tend to spend additional income on staples, marginal quality-of-life improvements and servicing past debt. While this spending (increased aggregate demand) can't be bad, it doesn't necessarily distribute the capital _efficiently_.
Meanwhile, as you put, the high earners who "save" (read: invest) their excess income are precisely those who stimulate the economy effectively, as they are typically more able to efficiently allocate investments. I make this broad-brush assumption based on personal experience and some research I read years ago I don't have the time to look up right now. But basically think about this: if you had $100 to invest, would you rather ask a hobo on the street or Bill Gates (let alone Ray Dalio)? This "sophistication factor" is relevant, I believe. Add in the fact that lower-income consumers are almost certain to spend the excess capital in a predictable but not necessarily efficient way, and it's fairly easy to make the argument that aggregate demand would best be created by a.) efficiently distributing capital to b.) create new and profitable enterprises that c.) create demand both domestically and internationally, and d.) purchases are made (demand is created) for those innovative new products/services using e.) the money earned by workers paid by the companies that just created them. (f. what a mouthful.)
Now we've not only increased demand but added to the whole pie via foreign trade. And gets us back to the point mentioned above that the quality of what we create directly impacts demand for it -- and you can't really get around that fact either.