There's really no 'agenda' behind any of this - for LGBT people, its largely because its one of the few mediums where independent individuals can truly express themselves without worry of institutional discrimination - at least in most cases. There's no agenda behind these comics beyond simply wanting to recognize that LGBT people exist, and that's okay and should be celebrated and welcomed, not tossed to the sidelines. I should know, I'm LGBT myself, and am friends with various LGBT artists and knew various comic artists.

For the "SJW" crowd, the more politicized comics are easy to distinguish from the cut and dry stories, but it ought to be noted that politicized media is hardly a new thing. Various philosophers frequently illustrated their points with works of fiction, for instance Jean Paul Sartre, or even Ayn Rand (if she can be called a philosopher lol). Fiction is just another means to get ideas across, and considering that just about everything that has a degree of subjectivity in it is going to be influenced by the political views of the average Joe and the author - whether its realized or not - it isn't something that's particularly unique to the "SJW" crowd. There's plenty of good reads on the relation of visual media and political activism.