The issue is this: They want inclusion in a church recognized marriage, and they don't want anyone in the world to be able to say, "Sorry, um, we don't want to share this thing we have with you guys, it's not what we made this for."
Essentially, imagine you have a room to play nintendo 64 with your friends on campus. That's great and all, over time some other people say, "Hey, can we use that room too?" and because they want to play 64 too, you say, "Sure!" and soon, most everyone is playing nintendo 64 in your room.
Someone, one day, wants to play Wii, so they say, "Okay, well, we don't like wii, so you can have your own room to play wii."
Then, they start getting angry, because while they don't want to play Wii in their own room- they thing the N64 kids should have to let them play a new game in their room, because they got raised on N64 and don't want to be considered different. They don't see Wii as any different to N64, and lots of people don't- most people play lots of video game consoles these days, and don't really care, and they can all have their own rooms, but the gang who made N64 room are saying, "We don't want you to call the Wii room the 'N64 Room!' as well, or do it in our room... just make your own room, and brand it as your own thing, please.'
They see being given their own room and not being allowed to use the structure of the N64 room as telling them they're different, but they don't see what they do as different, in spite of the fact that they wrote, pretty clearly, 'this room is for N64 consoles'. They say that their console is Nintendo too, so what's the difference?
When you're bisexual, you see the queer community and the straight community, and get exposure to both sides, and start to realize that gay marriage isn't about wanting to get married; it's about trying to get these people to stop seeing, at their most fundamental level, any difference between retro things, the way you've 'gotten used to', and something new, even if it's weird and seems a bit unnatural/unwieldy to get a grasp on.