To equate rights, you have to establish identity.The law trumps personal beliefs about what marriage is, has been, or should be.
Legally, marriage it is a fundamental right of all persons.
The only eligibility requirement for fundamental rights is being human.
Reasonable restrictions may be made only when a compelling and legitimate governmental interest can withstand judicial scrutiny. Most can agree with the courts that reasonable restrictions include age, ability to demonstrate informed consent, and not being closely related or currently married. Within those limits, gay people qualify. Gender restrictions have been shown to be irrational and harmful.
Procreation ability has never been a requirement for marriage, and therefore fails as a legitimate excuse for denial of equal treatment under the law. Yet even that irrational excuse for discrimination ignores the fact that gay people can and do reproduce, and are raising children either biologically related or adopted.
Denial of equal treatment under the law provides no benefit to opposite sex couple families. It only harms same sex couple families needlessly.
At the most basic essence, marriage is a cross cultural constraint on evolutionary mating behavior.
Gay couples are clearly a defective contradiction to mating.
If you want to dumb down marriage to a friendship, you leave the distinction of mating behavior with no term, and redundantly equate marriage with friendship.
Simply silly stupid.