Now that LGBT rights have gotten to the point where they have a legitimate voice in society, it's hardly surprising that some people abuse the platform they're given. Look at this site's general disdain for "SJWs." It's not "social justice" that people on this site hate, it's raving dogmatists who reduce everyone to a set of convenient labels.
I find it frustrating that "allies" nowadays seem to jump on social justice bandwagons to find new things to be outraged about: straight people being outraged for LGBT people, white people being outraged for black people, and so on and so forth. It's not that these "allies" want to combat social ills and improve the human condition, it's that they want an outlet for their righteous indignation and meaningless bluster. They want to shout down people they childishly view as "evil" without listening to the argument.
If you're looking at a cause from the outside, the best thing you can do is to approach the cause in an even headed way and listen to people rather than jump to conclusions and start shouting. The "FCKH8" group is notorious for this sort of behavior. The LGBT struggle for solidarity and equality is a solemn and difficult issue and it's not something that can be reduced to a "good-vs-evil/us-vs-them" pissing contest.
In the same way I'll never know what it's like to be a black person and I'll never know what it's like to be brutalized by police officers on the sole basis of my skin color, I'll never know what it's like to be ostracized because of my sexuality. I'll never know what it's like to be a transsexual person who gets called a "monster" because of their struggles with gender identity. No matter how many books I read and stories I hear, their reality will never be my reality and so I should never get outraged as if I were suffering like they are. The role of the "ally" is to listen and seek to understand, to rectify one's own behavior in order not to participate in hurtful behavior, not to get outraged and yell at people.
From the other side, I have an issue with the American conception of religion that makes it seem like every religion is like one of the theologically impoverished Protestant offshoots and that everyone who opposes LGBT marriage is an evil bigot. In its purest form, religious apologism is about defending something that comes down from on high. While TV Evangelists rail about how "gays are an abomination," Catholics (at least the ones who haven't muddied their faith with various American Protestant misreadings and misunderstandings) defend the institution of marriage because marriage is an inherently religious concept that comes down from above. Church teaching makes it very clear that it is the act of sin, not someone's identity, that needs to be challenged, and furthermore that hate speech is not the way to defend higher truth.