Tony Campolo interview on the February 4, 2008 showing of The Colbert Report.
Campolo is a representative of a subgroup of evangelical Christians who believe that the Religious Right has gotten it wrong. Campolo, and those he describes as Red Letter Christians are interested in relieving the suffering of the poor and support gay marriage on the basis that Jesus would want civil equality for all people and would not want any person oppressed. They may theologically still believe that homosexuality is a sin, but don't see that as appropriate reasoning for denying people civil equality.
Make no mistake that Campolo considers homosexuality a sin, a problem. Based on sermons he has delivered, he believes that true gay Christians must remain celebate. That point of theology aside (and, yes, it's a pretty significant difference in theology), he at least promotes the idea that gay people should be accepted as any other member and shames the church for failing in its mission and ostracizing instead of embracing anyone desiring to be loved by God. He also clearly makes the point that sexual orientation is not likely to change and that no simple answers exist as to why people are gay. Even though I strongly disagree with his strict reading of the Bible, I am glad to know that there are evangelicals out there who advocate for social justice and getting back to the love of Christ.