Guardians are necessary for children and abnormal adults, because they cannot make responsible choices for themselves.
Libertarians argue that no normal adult has the right to impose choices on other normal adults, except in abnormal circumstances, such as when one person finds another unconscious and administers medical assistance or calls an ambulance.
Abstraction is a mental process we use when trying to discern what is essential or relevant to a problem; it does not require a belief in abstract entities.
Libertarians recognize the difference between adults and children, as well as differences between normal adults and adults who are insane or mentally hindered or retarded.
Equality of rights means that some people cannot simply impose obligations on others, for the moral agency and rights of those others would then be violated.
What libertarians assert is simply that differences among normal adults do not imply different fundamental rights.
Libertarians recognize the inevitable pluralism of the modern world and for that reason assert that individual liberty is at least part of the common good.