No… we only come to this conclusion because we think of economic cost and benefit in monetary terms, and that “rationality” is somehow distinct from mores and emotions. Economics is not about money, it is about value. To a normal human being, murdering someone is inherently costly, because it violates our entrained mores and probably some fundamental mammalian instincts. Just as the benefit and enjoyment I get out of paying lower taxes is weighed against the cost of living in a country with decrepit and inadequate infrastructure, high crime rates, and a general level of human suffering that displeases me.

What puts someone on the spectrum between asshole and psychopath is when normal human social relations are no longer part of their (economic) value system.