I've heard this "you can choose one but not the other" argument for years, and it reveals some incorrect assumptions about religious beliefs. Ask religious believers (or non-believers) if they can just up and choose the reverse. They can't, at least not while remaining true to themselves, which is the same threshold that is used when celebrating a person's coming out.

You might counter that religious beliefs shift more easily than sexual orientation. The prevailing narrative used to be that sexual orientation is totally static. It was useful and effective to frame things this way in the fight for gay rights; it asked, "Why punish someone for something they can't control?" But now that we're at a point in history where every brand under the sun is comfortable running Pride marketing campaigns, what was once an open secret is now more out in the open. LGBT folks have become more comfortable acknowledging that there is indeed fluidity and spectrum when it comes to sexual preferences, orientation, and gender identity. That doesn't mean that a person's orientation can be forcibly changed, but there is an acknowledgement that preferences can sometimes change organically, and we see that with religion as well.