As someone who regards the first five books of the Hebrew Bible (Gen., Exodus, Lev., Num. and Deut.) as the sacred Word of God given to Moses, the foundation of my moral character, and the touchstone of my every action from the time I open my eyes in the morning to the time I lay down for sleep, I find this rather painful and offensive. As a professional advocate, I find it really bad advocacy. As someone actually familiar with the literature and the historic context, I find that most of the material circulating is as full of abysmal ignorance and hate as they project on their opponents.
I initially thought about writing a lengthy post to dispel some of the most common offensive stereotypes and misconceptions, but decided this would take just too damn long. I will simply note the following:
(a) the fact that a small number of people who support a position are hate-filled ignoramuses does not make the entire same sex marriage movement an anti-religious movement, nor does it make everyone else associated with the same sex marriage movement intolerant a-holes; (and yes, this point is generalizable)
(b) Many people who I know are not intolerant a-holes point to and/or circulate some of the most offensive material. I take this not as a character defect, but as the natural human trait to chose sides and view that which comes from my side favorably and that which comes from the other side unfavorably. This leads to --
(c) So if you are tempted to pass this stuff along, you may want to make a brief check on whether you really agree with the entire sentiment expressed or not. Sure, it's useful to point out that the Bible uses the same word toeivah (usually transalted "abomination") for man-on-man sex and for eating unclean food. That at least raises the very legitimate challenge of why should one verse be observed and the other not. But continuing on to the litany of everything the Bible permits that offend modern sensibilities (e.g., slavery) would not seem to have any purpose other than to say the Bible is a vile book and those who use it as a code for behavior and ethics are equally vile.
People are certainly entitled to hold that opinion and to evangelize them to the world, but that is a much broader set of issues than same sex marriage or even homophobia generally. If you are someone caught up in the moment retweeting or reposting someone else's "why using the Bible as the reason to oppose same sex marriage/justify homophobia is stupid" material, you may wish to consider whether the material you are retweeting or reposting actually conveys the broader view the the Bible is a vile foundation for a code of modern ethics and whether that is, in fact, the sentiment you wish to convey.
At the same time, I'm going to keep assuming that people who are my friends and who I don't think share that belief don't intend to convey that broader message and won't take offense. Those of you who do believe the Bible is a vile foundation for modern behavior don't bother me either, although why you chose to remain my friend when the halacha (Jewish law) is the foundation of my behavior is your own business.