In nature children come from a man and a woman coming together in a sexual union. It is a natural obligation that the parents care for their child. That is family. It requires commitment and ongoing active caring.
The core of the family is the committed, covenanted union of a woman and a man. That is marriage.
It is unnatural for same-sex persons to attempt union because there is no complementarity between same-sex persons. There is complementarity between a man and a woman.
The foregoing is true unless there is no definite human nature per se and human beings, having no definite innate nature, are malleable and can be formed into anything by choice. However, the objective reality is that human beings do have a definite nature and human nature is not malleable. The idea that we can make human nature anything we want it to be is false.
Therefore, it is a categorical mistake to hold that same-sex relationships are the equivalent in nature to marriage. To pretend otherwise does not change reality. To force anyone or any business or institution to accept and support the false notion that same-sex relationships are the same in nature as marriage is an attempt to force a falsehood on society. People in same-sex relationships do not have the right to have their relationships made legally equivalent to marriage because it is not marriage.