I agree that Catholic moral teaching is a great place to start and to begin the conversation. 

BUT...

I'll bet you think that's also the best and, dare I say only, place to END the conversation. If so, then it's not an honest educational intra-faith conversation you agree to. 

Are you open to learning, to enhanced understanding, to admitting others might have a point or two, to seeing an other side, to appreciating the experiences of others, and to changing your mind about what are the essential and non-essential things re the teachings about human sexuality?

We--on the Right, on the Left--shouldn't fake it, and enter into a conversation if we preclude learning and growth as  outcomes.   

I repeat the Wooden Law, learning is what happens after you think you know it all. Are you part of the learning process? Or are you closed to conversations that can educate you? 

 Do you already know it all? 

Do you seek a conversation, or do you want a pledge of conformity and homogenization?