Some collective values arise out of the combination of subjective preferences. For example, most of us may individually prefer to live somewhere where everyone has access to an education, so we establish this as a collective preference. Social choice theory studies ways in which subjective preferences may be combined that way. Also relevant is the notion of a public good -- a good that one cannot prevent others from enjoying; these are often vulnerable to free-riding. For example, everyone may prefer streets that aren't littered with trash. Even so, a (selfish) individual may prefer to litter because the impact on him personally is not so great and it's very convenient to litter. But if everyone prefers trash-free streets, then not littering is collectively preferred (which we can then try to enforce through fines, etc.). Thus, even if people individually would litter if not restrained from doing so, it may still be the case that the collective preference against littering arises from subjective preferences (because we all strongly prefer for other people not to litter).
This leads to the question of whether every collective value must be justified based on aggregating preferences expressed by individuals. One can try to find counterexamples. For one, one may argue that the collective should also take into account those who cannot express their preferences -- animals, babies, future generations, etc.