“A homosexual has the right to marry.” The ABC’s of Catholic Doctrine By Lianne Tiu

There are homosexuals who have previously been in legal (opposite sex) marriages; and there are people who have had homosexual relationships, renounce their behavior, and marry the opposite sex. Both cases show homosexuals who have exercised their right to legally marry.
The fundamental “right to marry” is a right that rests with individuals, not with couples. Homosexuals have exactly the same “right” to marry as anybody else. There are legal restrictions, however, as to whom they can marry. A homosexual, as well as a heterosexual, cannot just marry any partner they like. To be specific, anyone of marriageable age, regardless of his sexual orientation, is legally disqualified from marrying a close-blooded relative, a child, a person who is already married, or a person of the same sex. Restrictions are intended to protect people from harm. Removing restrictions brings about countless negative consequences. For example: Children from incest have a greater risk of congenital disorders, death and disability. Girls in child marriages are more likely to suffer from domestic and sexual violence, devastating mental health consequences, and death due to complications from pregnancy and childbirth. Children from divorced parents are more likely to experience deep emotional pain, poor social skills, low self-esteem, learning problems, higher divorce rates, to name a few. Children from same sex marriage are more likely to experience sexual confusion and are deprived of a proper environment for a healthy development- psychologically, mentally, and physically.
There is no discrimination here – the restrictions on the choice of marital partner apply equally to every individual in order to ensure the protection of everyone.
Yes, a homosexual is free to get married, but not just with anybody if the marriage will cause harm to an individual, to other people, or to society.

(Reference: “What’s wrong with letting same-sex couples legally “marry”?” by Peter Sprigg; Same-Sex Marriage is Harmful to Children by Trayce Hansen: Wikipedia; )