Why Is It Important for Legalized Marriage to Be Open

Why is it important for legalized marriage to be open to both same-sex and mixed-sex couples?

A) Having an institutionalized form of social support for relationships is associated with positive mental and physical health for individuals in the relationship.
B) It would help even out the differences between same-sex and mixed-sex couples.
C) It is not necessary; an institutionalized form of social support does not contribute to the wellbeing of couples, regardless of whether they are same-sex or mixed-sex.
D) All couples should be able to file joint federal tax returns and enjoy other benefits of marriage.