Traditional marriage was systematically persecuted in the West until it became extinct. It still exists, however, in Africa, the Middle East, and Asia.
Humanity has been engaging in traditional marriage for 300 000 years, long before the church grabbed control over marriage. In fact, even for the first 1600+ years of Christianity, only traditional marriage existed.
You can find an interesting explanation as to the difference between Christian and traditional marriage in Africa in the following link:
The difference between Traditional and Christian Marriage
Christianity is no longer in a position that it can violently persecute and stamp out traditional marriage like it originally did in Europe.
The church still does not recognize traditional marriage, however. If the clergy does not exercise total control over the marriage, then it considers the marriage to be void.
In my opinion, it works exactly the other way around. Only traditional marriage is valid and legitimate. It is marriage in church that is void.
The scriptures do not give control over marriage to the Church. By recognizing church authority over marriage anyway, Christians are extending the authority of the Church beyond what is mandated by the scriptures and beyond what is reasonable. The Quran explicitly condemns this behavior:
By giving control over marriage to their clergy, Christians associate their clergy as partner to God. By giving control over marriage to the government through civil marriage, Christians associate their government also as partner to God.Quran 9:31. They take their priests and their anchorites to be their lords in derogation of Allah, and (they take as their Lord) Christ the son of Mary; yet they were commanded to worship but One Allah: there is no god but He. Praise and glory to Him: (Far is He) from having the partners they associate (with Him).
There is no worse sin in Islam than giving that kind of power to other humans.
Perhaps you understand now why Islam resonates so much in libertarian ears. Libertarians simply do not want to give that kind of power to other people. In Islam it is even a blind foundational belief that you should never do that. It is even considered the worst sin on earth.