There's an additional, even more direct, harm as well. Last week, a county in Oregon stopped issuing ANY marriage licenses, including to heterosexual couples, because they were prevented from issuing them to homosexual couples. This could ultimately destroy the legal institution of marriage, which in turn has the potential of destroying our society!
You are correct. It could injure the legal institution of marriage.
Holy matrimony, however, will forever be under the purview of the historic Christian (orthodox) Church.