certainly teasing out the most rational in all cases requires many more words than i can possibly write, but i think we're also looking at it from different perspectives. what's seemingly rational for the investor in the short-term may not be rational in the long-term or for the resilience and longevity of the economy.
the marginal utility of the next dollar tends to zero as an investor's wealth increases (assumed to be someone above the median in wealth/income), both to the individual and to the economy, but the economy has no signal to indicate that. it's assumed that more is better, greed is good, but that's clearly not the case from the many other, sometimes indirect, socioeconomic signals we have around us. those low-utility dollars tend to be less well-invested than higher utility dollars, even if the returns are net positive. for an economy, especially one predicated on the idea of being highly efficient at allocating investment, that's problematic.
further, washing otherwise fundamentally sound businesses (including tech and real estate) in too much money distorts their ability to discern the next best, positive-NPV (and sometimes counterintuitive) investment. in fact, studies show that managers will time and again allocate capital to negative-NPV investments if it provides personal gain (both economic and non-economic) at the expense of others.