Secular gay marriage and secular adoption by gay parents should be allowed in the United States. Religious organizations should be exempt from any government requirement to allow gay marriage or forced adoption by gay parents.
Homosexuality may not be morally acceptable to religious organizations but many other human activities are also unacceptable to various types of religions but these people are still allowed to adopt. The danger to religious organizations and individuals is that government will be used to force an unacceptable secular morality on religious marriage and adoption.
I have heard some news reports that Churches in Great Britain are starting to be forced by law to accept homosexual marriage. Businesses such as bakeries are being forced to participate in homosexual marriages in our own country or face severe fines. Forcing religious adoption agencies to grant adoptions to couples opposed to their religious beliefs is probably next. That is unfair and wrong. People should be free to choose what they want to do and what organizations they want to associate themselves with. You are free to leave religious organizations but you are not free to impose your own values on others by using the guise of the government.