From Bryan Caplan What’s Wrong With the Rationality Community,in which he criticizes utilitarianism and consequentialism:
The first is consequentialist (or more specifically utilitarian) ethics. This view is vulnerable to many well-known, devastating counter-examples. But most people in the rationality community hastily and dogmatically reject them. Why? I say it’s aesthetic: One-sentence, algorithmic theories have great appeal to logical minds, even when they fit reality very poorly.
Capan’s argument against utilitarianism is weak
He uses an example of a hypothetical ‘slave society’, which has a higher total utility but an unequal distribution, to refute utilitarianism on the grounds of being unjust. But he ignores that individuals (such as criminals) can take away utility from others (which is a much more relevant/applicable example). So replace ‘slaves’ with ‘criminals’ in his example, and utilitarianism makes more sense (because criminals don’t deserve much utility).
Regarding consequentialism, consequentialism (and related utilitarianism ) is an inescapable part of any developed society.
Some are unsettled by the idea that the value of a human can be reduced to a number, but if you have insurance (health, auto, home) – that is exactly what it is–an attempt to assign a monetary value to a human life in order to price a policy, yet when the argument is framed differently, these very people become mortified at the premise that human life does indeed have a finite value, or that some lives may be more valuable than others. ‘Pro life’ taken to its extreme would be mean no war and no death penalty – both positions many Republicans, who identify as ‘pro life’, support. So why does this contradiction exist? I suppose because they rationalize from a consequentialist standpoint that the possible loss of some innocent lives (the occasionally wrongly executed individual, soldiers dying, or collateral damage) indirectly serves a ‘greater good and more utility’ (preventing more deaths both directly and indirectly), justifying this trade-off.
But such fears may be irrational, because utilitarianism and consequentialism underpin society and the economy on a day-to-day basis. Utilitarianism is simply a way of quantifying the risk/reward analysis of decisions by choosing actions that maximize utility and minimize costs, such as a business ordering in-demand ‘units’ and discontinuing ones that don’t sell. All else being equal, a business that does not maximize utility is at a competitive disadvantage against one that does.
You cannot always derive an ought from an is, but sometimes you can, such as when there are externalities involved. A consequentialist libertariarian, ancap, or minarchist could oppose slavery on the grounds of violating the NAP and the ‘golden rule’. Same for criminality, which is a violation of NAP due to external costs on society imposed by criminals against people who don’t consent (the question of consent is complicated, and Scott discusses this in further detail) to being victimized. For example, if a gunman is threatening a group of people, homicide by police is justifiable from a consequentialist perspective (ending one life to potentially save many), and this actually happens. The ‘trolley car’ would violate NAP, but consequentalism can be invoked from a deontological standpoint if there is an obvious aggressor such as a gunman (in the case of the trolley car, the fat man is not an aggressor, nor did he consent to being pushed). This is how consequentialism can be merged with the NAP, while bypassing the ‘trolley guillotine’. Abortion is more difficult situation, which is why the issue is so heavily debated, whereas the morality of justifiable homicide against spree shooters, is less contentious of an issue.
But the problem is, the NAP invokes the Sorites paradox: when does an annoyance become aggression? What constitutes ‘consent’? And how much should society and or the individual retaliate against aggression? For severe crimes, retributive punishment is easier to justify morally. Punishing smaller crimes is harder. However, small crimes perpetuated many times by thousands of individuals, adds up to a significant social and economic cost, justifying prisons to warehouse these people in a humane manner consistent with NAP, yet in the spirit of consequentialism and utilitarianism, improving total social well being by segregating these people from society.
Often, arguments against utilitarianism and consequentialism involve absurd hypotheticals (excluded middle fallacy, as well as slippery slope). Consequentialism does not imply moral nihilism.  Now Peter Singer Argues That It Might Be Okay To Rape Disabled People
It can lead you to believe that it’s less morally justifiable for a couple to remain childless than it it is to murder an elderly homeless person in their sleep (because failing to create a potential happy long life is worse than taking someone’s unhappy short remaining life).
But the homeless person is not an aggressor, so murdering him would violate NAP even if utilitarianism condones it. Overall, the United states (and most other governments) have a mix of deontological (rule-based) and consequentialist ethics, but in a way compatible with NAP (which means no pushing fat men to their deaths or murdering homeless people). But is denying costly medical care, however, for a person with a terminal prognosis the same as murder? That is harder to answer, and given America’s surging heath care spending, it’ something that may need to be considered further.
 At the extreme, Stalin’s purges could have been justified on the grounds of consequentialism, to promote what Stain rationalized as the ‘greatest good’ for his people even if millions had to die in the process (although this obviously violates NAP, and given how many people died and the famine and economic collapse, such purges most certainty had a net-negative utility, violating utilitarianism principles). The perceived utilitarian tendency to reduce the totality of humanity in to into quantifiable ‘units’ of economic value or economic ‘agents’ whose utility must be maximized at all costs, irrespective of ambiguous concepts like morality, could explain why utilitarianism may be off-putting to some. Extreme example, however, don’t refute utilitarianism. Deontological ethics, or probably any ethical system, can be contorted in a similar manner when drawn to their most extreme logical conclusion.