That's understandable and I kinda knew that beforehand, thus the "rules" as a gentle reminder to keep in the back of your head.
Rules? HERE?! Surely you jest! (And surely they joust here.)
As you have seen any topic you start here can quickly be turned into a debate, with both sides of the argument rushing to the battle lines, armed to the teeth with the bible verses they use to defend their side and cut down the opposing side in a given debate. However, I would like to answer your original post. How does one witness to them?
Just like any salesman talks to someone. You explain what you have and why they need it. Nothing more or less.
There's a company called Earthworks that makes really expensive microphones. I mean really expensive - as in, their measurement mic is $600. Microphones for recording professional singers are more expensive. There's also a company I won't mention that makes a $50 knockoff. I have never seen a commercial from Earthworks talking about how shoddy this knockoff is and why I shouldn't buy it. They just make a really good mic and advertise its qualities and quality. Some buy it because they want that kind of quality. Some get the cheap knockoff. But the ones who spring for the Earthworks mic get one good microphone. But Earthworks doesn't spend a lot of time explaining why the knockoff is so bad. They just explain why their microphone is good.
There's a guy I work with that I have been taking to work lately, because he lacks transportation. He's not a christian, he talks a lot about how he got drunk the night before, he might briefly allude to last night's activities with his girlfriend. I don't spend a lot of time talking about how what he does is wrong. When I talk about God I talk about what I know, what I benefit from being a Christian, the peace I have in this really messed up world. I don't talk against the competition, I talk for my product. Last Sunday night he came to church (and weeeee, did we have a good service!) He said he wants to come again this Sunday night.
What if a homosexual brings up his homosexuality? What if he gets confrontational about it being a sin? Well... what if someone called up Earthworks and ranted about how expensive their measurement mics were? What if someone went on about the knockoff? What would it matter to Earthworks? Such a person is argumentative and looking for a fight. Would you expect the Earthworks employee to get in an argument with this person?