Believing that morality is subjective does not mean that you can't enforce a certain kind of morality on a group of people, actually.
Before I start anything, I'd just like to define the way I use certain terms. Morality is essentially a code of conduct, a way in which people should or should not act in general, or in various circumstances. And something that is objective would be something that is independent of human thoughts or feelings.
Objective morality, when normally used, denotes a set of rules that everyone should obey, regardless of social class or status. It is, in Stefan Molyneux's words, universally preferred behaviour. If it was wrong to kill, you'd be in the wrong for killing someone, no matter who you were. He also stated even if people did not comply with it, it was still considered objective, in the same way that mathematics is still a workable, objective system even if a person didn't follow the steps involved to get a correct answer.