So, maybe I'm overthinking. Those two sentences read as if personal liberty is important, but LGBT marriage somehow impact others' personal freedoms. This is based on my knowledge that conservatives tend to be anti-lgbt marriage rights.

Maybe it's the grouping of conservatives and libertarians together. Maybe that's where my head gets lost.

Libertarians are complicated.. in my experience they have mix of liberal and conservative values.

Take private property as a canonical example. Private property is good from both liberal and conservative perspective, but for different reasons. Liberals like private property because it confers more freedom to individuals, while conservatives like it because of its hereditary nature, as a reward for being good manager. These are two different values. (Oh and BTW, Marx was one of the first people who pointed out this contradiction, if you reward capitalists with property for doing good, eventually you're gonna run out of it..)

Well, in the United States LGBT marriage was instated via an application and extension of customary law, not any statute from Congress or even any overt politics. I see this as being quite compatible with conservative and libertarian values, seeking to remove undue interference from personal lives as much as possible. I'm not sure why you would disagree. Progressive activists may see the political process as the only way of achieving "positive" change, but that's a short-sighted point of view.

That's what I'm saying. In the US, conservatives actively worked, and still work, against personal liberties in terms of LGBT marriage rights. That was my point.

Be cautious of the definition trap.

People have different definitions of marriage. One person ‘defending’ one definition looks like ‘actively working against’ another definition.

E.g. in some cultures, by definition, a marriage isn’t valid without a male/female sexual act (the only kind that can lead to procreation, by definition). This axiom is held by over a billion humans for example.

LGBT marriage, at least in the United States, is a legal definition that need not have any bearing on how 'marriage' is understood in any other context. It came about purely as a legal hack, to address the needs of people who sought some legal acknowledgment of their stable companionship. The existing law and custom provides this wrt. "married" couples, and this was simply extended wholesale by sort-of pretending or establishing by fiat that two people can be 'married' no matter what their gender, as far as the law is concerned. It's a sensible mechanism that has plenty of other uses in law and policy.