Well, most things improve when allowed to change. With religions, especially islam, that is not possible, since muslims believe it to be the true word of god, so it can never be wrong etc etc.
But if something is not allowed to change, then no improvement is possible. For example, in science, it is always stated with pride that theories will be changed if new information comes along. The power of most human knowledge comes from the fact that they were willing to change old ideas if better reasoning came along.
Laws and even constitutions are modified to make them better. So is every branch of knowledge.
Now these people you are talking about may have many reasons to claim that it is OK in islam. One of course, is to gain social acceptability. And this is not new, there are many things, even in islam, where some muslims feel something it islamic, and some feel is unislamic. These homosexual people would still want to consider themselves muslims. Just because they are gay, they wouldnt want to immediately abandon the religion they grew up with. Because religious beliefs are emotional, and they have emotional reasons to keep considering themselves muslims. So they would want to believe that they are not committing a sin by being true to themselves.
Another reason is social acceptability. They would want more people to believe they are not doing anything unislamic, so that they dont face the prejudices and hatred that comes when people think they are defying their religion.
If you think about it, there are many reasons why they would want to argue that it is compatible with islam. (Or whatever religion they follow, if that religion prohibits it.)