Why Gay Marriage Should Remain Illegal in Certain States

Read the following passage entitled Why Gay Marriage Should Remain Illegal in Certain States, and then answer the following questions.

Why Gay Marriage Should Remain Illegal in Certain States

If we prohibit marriage between same-sex couples, we will maintain the institution of marriage as it was intended to be—between a man and a woman for the purpose of love, commitment, and reproduction. It is clear that the institution of marriage is maintained, because people are getting married out of love, to express their commitment for each other, and are having children at a faster rate than ever. Because these are valuable goals, we should continue to ban gay marriage to continue our success in maintaining this important institution.

Put this argument in standard form. Is the argument valid or invalid?