In his press conference just now, the president-elect made the expected argument in favor of Rick Warren -- basically (paraphrasing) there are a lot of opinions in America and the inauguration will reflect that.
However, an opinion like Warren's -- comparing same-sex marriage to pedophilia -- doesn't deserve a seat at the big boy table. People like Warren are obviously entitled to their opinion, but that doesn't mean we should give such quackery any more deference than, say, moon landing deniers.