No, actually we are not but I will play.
It is not adequate because the current marriage license sets up for two people to be each others closest relative. It says that the woman will make the decisions for the man and the man will make the decisions for the woman when one of the two is not able to make those decisions hisself/herself. It can easily be changed to allow a different man to replace the woman or a different woman to replace the man. The same does not work when you have more than two people involved because the marriage license does not get into specifics for any couple, it simply states which two people will be responsible for the decisions of each other. The same does not apply to when you have more than two people involved, because the current rules are specifically set up for two people, but the gender of those two people will not affect how those rules can be applied.
Also, your example of two guys robbing a bank, getting married, and being protected against testifying is wrong on so many levels. First of all, they would have to be married to each other before they talked about the robbery at all, because the law only protects them from testifying on intimate relationship conversations that took place during the legal marriage. Second, they wouldn't be called to a stand to testify against each other if they were both involved in the crime anyway, because that would set them up for self incrimination, and is not allowed.
BTW, I have stated many times that there should be some marriage contract available to polygamous families that gave them an opportunity to make them all family. It can't work with the current contract however, and it is the couples that want this who have the responsibility for coming up with a way to make it work for them, not the government. The gay community has it easy in this regard since the current marriage contract works fine for their relationship with one small change of adjusting the gender blocks of the marriage license so that it can be either two men, two women, or one man and one woman. No change in the actual application of the current marriage contract is necessary.
Now that I have provided what you asked for (again), you can answer some of my questions. Instead of going off on things that I never brought up in this thread.