Effects are environmental, mainly from bigoted morons like several people who've posted in this thread.
Legally, this and all other legal debates about same-sex marriage are moot. In 1967, in one of the concurring opinions to Loving v. State of Virginia, the Supreme Court ruled , that every US person had a right to marry someone (as long as consent is able to be legally obtained and obviously not in cases of bigamy) and is due all the legal rights and protections of marriage. The right is not given in the constitution but is implied as a natural right (legally defined as fundamental rights granted by God/nature, not society) and is covered under the Right to the Pursuit of Happiness.
Based on that definition and the natural rights guaranteed as the foundation of this country, denying someone the right to marry is morally equivalent to murder, slavery, and wrongful imprisonment.