It's about lust ... and most humans are prone to it (lust) .... gay or not. Many forms of lust.
1 Corinthians 6:18
Flee from sexual immorality. Every other sin a person commits is outside the body, but the sexually immoral person sins against his own body.
4202 porneía (the root of the English terms "pornography, pornographic"; cf.
4205 /pórnos) which is derived from
pernaō, "to sell off") – properly, a
selling off (surrendering) of sexual purity;
promiscuity of any (every) type.
sin is sin .... and we all sin .... Jesus will help us to overcome our sin ... any sin.
Just let them know what the word of God says ... and also that everyone (including christians) struggle with sin but that there is help for all of us through following Jesus.
Murder is a sin ... yet no one has a problem stating that it is. And even so, murder can be forgiven. Do they think it's "ok" to commit murder? Of course not. Well ... why not? It is harmful ... any sin is harmful ... and homosexuality is certainly not the only sin. Lying is a sin, stealing is a sin, idolatry is a sin, adultery is a sin etc...
1 Corinthians 6:9-10
Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived: neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice homosexuality, nor thieves, nor the greedy, nor drunkards, nor revilers, nor swindlers will inherit the kingdom of God.
We are all sinners. We are all called to repentance. We all need help and only that help comes through Jesus and it is a life-time commitment and all will stumble here and there.
God created us in his image .... to be righteous. Gods word defines what sin is .... states it is harmful .... one either believes/accepts that or not.
Point them to Jesus ... be kind ... and pray for them ... witness to them just as you would anybody else who is sinning.