And even ignoring that, Hitler and Stalin may be valuable as examples because they don't resemble strict utilitarianism, but they do resemble utilitarianism as done by fallible humans. Actual humans who claim that the ends justify the means also try to downplay exactly how bad the end is, and their methods of downplaying that do resemble ideas of Hitler and Stalin.

Can you provide examples of this? In my experience, while utilitarianism done by fallible humans may be less desirable than utilitarianism as performed by ideal rationalists, the worst failures of judgment on an "ends justify the means" basis tend not to come from people actually proposing policies on a utilitarian basis, but from people who were not utilitarians whose policies are later held up as examples of what utilitarians would do, or from people who are not utilitarians proposing hypotheticals of their own as what policies utilitarianism would lead to.

Non utilitarians in my experience generally point to dangers of a hypothetical "utilitarianism as implemented by someone much dumber or more discriminatory than I am," which is why for example in Yvain's Consequentialism FAQ, the objections he answered tended to be from people believing that utilitarians would engage in actions that those posing the objections could see would lead to bad consequences.

Utilitarianism as practiced by fallible humans would certainly have its failings, but there are also points of policy where it probably offers some very substantial benefits relative to our current norms, and it's disingenuous to focus only on the negative or pretend that humans are dumber than they actually are when it comes to making utilitarian judgments.