Most lefty bloggers object strongly to Rick Warren speaking at the inauguration. While I have no use for Rev. Warren's views on, well, much of anything, I think their objections are a serious mistake.
It's important to remember that "Gay Rights" dates only back to the 1970's. The changes in the acceptances of women, gays, and lesbians in my lifetime is phenomenal, and actually speaks well of humanity, which is saying a lot. This means that many, many people have changed their minds on the issue in what is by historical standards an eyeblink.
What does this have to do with Rick Warren? He is, among leaders of the religious right, one of the most moderate, and easily the most moderate person one with a big following. Many of his followers are likely to be even more reasonable than he is, and will be important allies on environmental and economic issues. If they can be persuaded to work with progressives on those issues, especially if they work alongside feminists and gays and people they won't know otherwise, they are more likely to change their opinion on the issues where we disagree. In order to get to that spot, though, we can't demonize them on that issue now. We have to give them space to change their minds.
There is much good to gain from allowing people to change their minds, and using persuasion rather than anger. The Right is forever pointing out that the Democrats never kicked out Robert Byrd, even though the senior senator from West Virginia was a Klansman in his youth. This is a silly argument on their part, in that there is no evidence that Byrd is still a racist. Byrd's legacy in the Senate is principally protecting the coal industry and hauling back as much highway money for his home state as possible, but the man has genuinely changed his views on African Americans. He doesn't and didn't oppose civil rights legislation, he doesn't make speeches about black inferiority, he just plasters his name on every scrap of concrete in West Virginia. Civil rights leaders understood that vilifying Byrd for what he used to think wasn't going to do any good, and accepted that he really had changed.
Rigid sex roles were typical through the 1960's. Lots of people who grew up even through the 1980's will have said stupid things about gays and women, and many of those things will have been published. Allowing Warren to speak without interruption will win many more converts than a pointless protest.