I’ll speak only for myself as a Christian. I can’t speak for all of Christendom.
It’s only sinful if acted upon, just as temptation to commit heterosexual pre- or extra-marital sex is sinful only if acted upon (either physically or mentally). It can result from abuse or natural tendencies.
It seems to me that many Christians often judge homosexual activity very harshly while being far more lenient towards, accepting of, or even participating in heterosexual fornication.
When completing a survey taken by our church on the topic, my wife and I responded that the church and congregation should treat an active homosexual no differently than they would treat a sexually active unmarried heterosexual.