. The author is arguing that no human being is without sin, all sin leads to spiritual death (separation from God), and all people therefore need a Saviour.
So, I don't think it would be a strawman to say that they do view homosexuality as sinful....
I'd wager that anyone frequenting this forum has at some point (if not constantly) looked at their own actions and weighed them. The way we treat others, our motivations, bad habits etc etc. What we measure them against is what we 'instinctively' know is 'right'. If our actions don't balance with this knowing, we experience dis-ease at some point, somehow. It may not be instant but it will show up in life. Those of us with a modicum of wisdom observe how this plays out and set about sorting our act out. Those with no wisdom, carry on creating dis-ease by acting against their inner sense of 'right'.
The wise are acting in harmony with their inner knowing at all times. They are harmonising with creation itself and actively participating in it.
Now, the Christian faith describes this as, sin. The separation from God spoken of is exactly what i just described. There is wisdom in the words. In the Christian faith the more you follow that 'rightness', the closer to God you become. Thing is, even if you are an atheist and couched it in terms such as 'getting true to oneself', it is impossible to do so without acting with all creation as your motivation. Selfishness would somewhat 'kill the buzz'. So it's the same thing for an atheist as a Christian.
But here is the difference. The atheist is free to understand that ramming your cock up another man's fun shute is only 'sinful' if you have acted against 'right' to make it a reality. If you gave the guy rohypnol then its a fair bet you just 'sinned'.
But a Christian, of a denomination, is not free to see this simple truth. They are taught that the act itself is a sin and dissent is not encouraged. The Christian of denomination has devolved their inner knowing to the inner knowing of God via a book. And that leaves them open to being fed bullshit that will most certainly keep them from 'God'. God would have an inner knkwledge of 'right' no?

God would know that making people feel bad, persecuted or outcast in any way would be 'sinful'.
I contend this is exactly what churches are for. To keep folk from God.
This is not to say that a Christian who has their own inner relationship with the teachings of Christ will not come closer to 'God'. This Christ chap certainly seemed to know a thing or two about 'right'

I'll stop now, could go on all night and me thumbs are hurting...