An Opinion piece in the New York Times this past weekend is well worth reading. The author, William N. Eskridge Jr. (a professor at Yale Law School), makes the case that the Judeo-Christian heritage is not uniformly against gay marriage nor sees homosexuality as a sinful state or set of sinful actions. Like it or not, many Christians are on each side of this issue, most claiming Scriptural support for their arguments.
In the process, he briefly outlines a few of the points I've written about on this site. From discussions of how conservative Christians have gotten interpretations wrong in the past (on race in particular) and how the current debate is not as clear from the texts as we might like today, it seems like a reasonable case to support giving freedom to those we may not agree with.