The government should get out of the marriage business. It is a private issue between people. If churches, sports clubs or celebrants want to host these unenforceable pledge parties let them. Marriage is a matter of morality not law.
There is almost no practical difference between marriages and defacto relationships at law. (Thorburn and I have argued this at length and agreed to differ).
If a group of blokes all want to get married thats their issue.