When a small group of people form a government and automatically include every other person within their power sphere (gang turf, nation state, boundaries etc.) without the explicit consent of some of those people, would you say at least some people are prohibited from doing what they wish to do?
Also, why do you think government should equally oppress gay people who want to be married ? Why should some people have the power to "approve" or "disapprove" of other peoples relationships?
My personal opinion on the matter is that marriage should not be tied whatsoever to government oversight. Taxation and representation thereof should be an individual requirement. The government should never "approve" or "disapprove" of any individual unless that individual has broken a law (that affects or even effects another's actions or livelihood). So in your example, gang members are free to stand on the street corners and throw gang signs all they want, but as soon as they sell drugs to someone or shoot someone in the face, they should be punished.
"I despise your killing, and raping"
"You're... despicable"
"Are you my judge?"
"It's just, ...you should be punished."
"I'm going to chop off your arm, are you ready?"