I did not say it is not equal, I said it is not the same. Define marriage. Then fix the problems that the definition will create if it does not mean what it has traditionally.
Marry two joints. Marry two parts. Marry two people? If you mean to change the definition, then there is more to change. I did not say y+3 is not equal to 9. I wrote y=6 6+3=9 then y+3=10 is not correct if you defined y=6 for all applications. If this is the way you define "y" then changing the definition creates a few problems. If two people want to spend the rest of their lives together, great. When it comes time to marry, then the definition should fit.