I agree with the position that state and federal governments should not have anything to do with marriage, they should only recognize civil unions for legal purposes including property, benefits, and issues such as medical care.
Those civil unions should be between any consenting adults.
The religious should be free to determine who can and can't be married under their religious laws, but these marriages will have no legal standing with government, only the civil unions will matter in the eyes of the law.
Divorce in the legal sense would involve ending a civil union, which could always happen even if a person's chruch refuses to allow them to end their marriage.
Employers, etc. would not be allowed to even ask about the religious martial status of employees, only about their civil union.
And why should the government grant benefits to people in certain types of relationships?
Property and medical care can be taken care of with medical proxy and a will.