From the New Yorker (go read the whole thing)
In hindsight, no one doubts that allowing business owners to discriminate against black people during the Civil Rights era would have denied them full equality and hampered desegregation. (Arguably, the continued tolerance of discrimination by private clubs also undermines desegregation, though club membership is less essential to daily life than shopping.) Similarly, allowing private discrimination against gay couples is not an exemption from a new rule of full equality; it is a compromise that allows inequality to persist. Proposals to let magistrates withhold marriage licenses have the same problems, with the added insult that the discrimination is effectively coming from the state. If officials can decide not to implement laws they dislike, then equality under the law—for gay couples, at least —is just a slogan.