Pastor Rick Warren thinks that it is a "humanitarian issue" and a moral imperative that homosexual couples never be granted the right to enjoy the same legal rights and benefits that heterosexual couples currently have in the United States. He advocates for Constitutional amendments specifically singling out and excluding them from the right to marry, so that not even a democratic majority vote could grant them equal marriage rights.
Here is Rick Warren, attempting to justify his call to discrimination:
Take note of how he explicitly lies and says that no culture, in 5,000 years, has granted homosexuals the right to marry. I guess that Canada does not have a culture. Spain must not have a culture, either. Same goes for Connecticut and Massachusetts. Mr. Warren seems to have either recklessly forgotten that these regions explicitly recognize homosexual marriages (which is just as bad as outright lying), or to have deliberately lied in order to bolster his point.
Also take note of how Mr. Warren tells another untruth, and says that no religion in 5,000 years has recognized the right of homosexual couples to marry. I guess that the United Church of Christ is not a religious organization. Same goes for the Unitarians. Mr. Warren has either recklessly forgotten their existence or deliberately lied about them.
In sum, Rick Warren is an asshole who advocates for institutional discrimination and tells lies to bolster his phony arguments. It's especially discouraging to see such bile coming from such a nice-guy facade (same goes for Mike Huckabee, who has compared homosexual marriages to bestiality and pedophilia).
It's sad to see that Barack Obama has selected Warren to deliver the invocation. I suppose, though, that most other major religious leaders would be making the same thin arguments in favor of the same discriminatory policies.
UPDATE: I also particularly hate that endlessly stupid language fetish: "We can't let 2% of the population change the definition of marriage." We all know that that's not the real issue. We're always altering state marriage laws and customs, to permit or deny no-fault divorce, common law marriage, interracial marriage, inter-denominational marriage, property rights, custody issues, etc. Marriage, as a legal institution, has always been in flux, and always will be in flux. Warren's "can't change the definition" argument is pure bullshit, and everybody knows it. What this is really about is people like Warren trying to avoid any kind of institutional recognition or acceptance of homosexuality (which has been around for much more than 5,000 years).
UPDATE II: Warren and Huckabee are like two peas in a pod.
UPDATE III: Rick Warren is a creationist, by the way:
Do you believe Creation happened in the way Genesis describes it?
WARREN: If you're asking me do I believe in evolution, the answer is no, I don't.