Not treating people as means to an end is a direct corollary of this principle; most of the time, barring true accidents or errors, to harm people means to treat them as a tool for our own values, instead of following theirs. Every crime, every atrocity, every conspiracy, reduces itself to fulfilling some people’s values at the expense of the victims’.
The maxim “the end justifies the means” can only make sense if you already seek to impose the rule of brute force, otherwise it is a logical impossibility. Moral justification for an action can only be located in the action itself and its context, not in some hypothetical future state. As says the Zapffe quote on my header, no future triumph or metamorphosis can justify the pitiful blighting of a human being against his will: I chose this quote as an apt restatement of “do not treat people as a means to an end.”
Independent confirmation of the principle is the fact that all radical positions have at their foundation a desire for some people to not be treated as means to some authoritarian end: people who are not part of the power elite (anarchism, anti-globalization), religious believers and those attacked by believers (anti-theism), women (radical feminism, anti-genderism), children (antinatalism, anti-pedagogy), all living species including humans (radical environmentalism). The flip side of this, of course, is that there are plenty of corrupt people who have used and continue to use these people as means to their ends, otherwise radical ideologies would not need to exist.
All hierarchies must necessarily use people as means to an end, because all hierarchies are predicated on superiors and inferiors. Inferiors must obey, and therefore surrender their value-system to that of their superiors. The values of the victims of these hierarchies are obviously equally irrelevant. Militaries do not waste any time examining whether their murdered victims valued the “freedom” supposedly being fought for, alcohol manufacturers do not spend money investigating the victims of drunk driving accidents, and male misogynists not known for their concern for female rape victims.
The consequence of routinely treating individuals as tools is objectification, literally associating individuals with tools. So you have the serious business expression “human resources,” living species called “natural resources,” the semantic association of women with nature. No matter what hierarchy you examine, you find absolute disdain and contempt for those lower on the ladder and desperate attempts to shut them up, indoctrinate them to devalue themselves, eradicate criticism in any way possible, and so on.
From an intuitionist standpoint, not treating others as a means to an end is a logical corollary to seeing other moral agents as being equally valuable as ourselves. This has a counterpart in the common sense notion of respecting others as you wish to be respected, and the Golden Rule.
So there are two basic tendencies in any society: one is the natural moral impulse to condemn treating other people as means to an end, which we might call legitimate crimes (murder, assault, fraud, etc), and another is the overwhelming power of hierarchies in molding thought, hiding its legitimate crimes (military crimes, police crimes, criminal collusion between the government and private entities, etc), and creating illegitimate crimes (heresy, treason and sedition, prostitution, drug crimes, evading arrest, etc).
This struggle between human rights and hierarchies typifies most of human history. This is why I sometimes say that there’s only two options, to be pro-harm or anti-harm. Of course every day situations are more complicated; but when you boil it down, every statist law, every State power, every claim of property is ultimately backed by the gun of the State; every religious maneuver and argument is backed by the wrath of God; every genderist rule is backed by ostracism, rape and murder. You can’t co-opt people “a little bit.”