I'm not trying to avoid the topic of sin in this discussion; just acknowledging that it's not an approach that we have to rely on exclusively, and that it's not always useful in trying to communicate. As a Christian, I recognize the sinfulness of the behavior, as you so accurately distinguish it from the feelings. Simply put, while the behavior is sinful, the brokenness behind it is just human. But unless we plan to engage in dialogue only with those who recognize Biblical authority (usually known as preaching to the choir), we have to reach beyond the sin aspect to engage someone who doesn't already see things our way. That's my main point.
They could care less about any religion that opposes their world-view.
Still super easy to refute homosexuality from a Darwinian / Evolution argument.