Help sorting through a discussion with my brother about marriage + wider topic of discourse with infuriating people

I don't really like my brother, he's extraordinarily arrogant despite having nothing to prove his competence in any capacity. He's 17 years old, has failed across the board academically and is good at nothing except playing videogames. He's rude, belligerent and impossibly disagreeable. He'll argue just for the sake of shitting on your opinions. Everyone who disagrees with him is an idiot, and all religious people are idiots. He cannot grasp the irony in him making such a statement.

Anyway. I don't value his opinion, and yet he has the annoying habit of getting under my skin with his way of appealing to radical subjectivity and individuality (he doesn't understand his points in those terms but that's essentially what he's doing) and dismissing any appeal to widely-held values or morality as essentially naive. I'm reasonably intelligent and have a good verbal IQ, but I'm struggling to get the message across and it's bugging me like you wouldn't believe.

I make a couple of essentialist claims about marriage. I believe that in the event of divorce, child support and sensible alimony rates support the institution of marriage and the family unit in society. If one party agrees to sacrifice future earnings to have children, they should do so without fear of financial ruin in the event of divorce. The alternative is that marriage becomes a game of contingencies, and that if you're planning a marriage as if it's not going to be permanent then it's not marriage. A marriage should be a unit of mutual responsibility.

This is, of course, a value judgment. Like marriage itself, it's not a natural fact of Being, a point my brother made in his own way. He kept returning to the idea of marriage as an 'artificial construct' and that people don't get married for the high-minded reasons I'm talking about, but he didn't seem to grasp that institutions uphold (or at least should) certain values as absolute, regardless of the subjective whims of citizens. When put into practice these values have real implications, and as such should be regarded as 'real'.

As I said above he began to insult my intelligence by implying naivety in my worldview. I start getting frustrated and in his eyes when that happens he's won. I have a degree of intellectual vanity myself and I ought to be more zen about these things but it's got to the point where I've begun questioning whether I'm even making sense. He's an impossible sounding board because he doesn't even really listen to your arguments.

Am I making sense? Does anybody have any advice for dealing with people like this? Sorry for the rant but I'm home from college for a few months so I've got to learn to live with this jackass and I'm already wasting too much time and energy with this shit.