The following scripture explain that there is a
leaving of the natural use of the woman, and a discussion can start by pointing out that no one is born without the application of the natural use. If there was no more people following the natural use, extinction would occur in a single generation, this can't be argued with.
Therefore there is that which is natural, so it follows that the other is not natural, is against nature, is not according to the design and natural order.
It is not far down that line where the mind takes a turn, not liking to have God in their knowledge, and they move into the reprobate mind stage.
Rom 1:27 And likewise also the men, leaving the natural use of the woman, burned in their lust one toward another; men with men working that which is unseemly, and receiving in themselves that recompence of their error which was meet.
Rom 1:28 And even as they did not like to retain God in their knowledge, God gave them over to a reprobate mind, to do those things which are not convenient;
Rom 1:29 Being filled with all unrighteousness, fornication, wickedness, covetousness, maliciousness; full of envy, murder, debate, deceit, malignity; whisperers,
Rom 1:32 Who knowing the judgment of God, that they which commit such things are worthy of death, not only do the same, but have pleasure in them that do them.
Rom 2:5 But after thy hardness and impenitent heart treasurest up unto thyself wrath against the day of wrath and revelation of the righteous judgment of God;
Rom 2:6 Who will render to every man according to his deeds:
Truth can only really be established by the scriptures, so if you try to discuss truth with someone that rejects the scriptures, you have no common ground, no point of contact that will help them. If anyone is willing to consider the scripture, you have a chance to help them.