Have you taken them shooting? It's never failed for me. I've had several friends with little exposure to guns, who understandibly were fearful from lack of experience with them. A perspective of never having had a gun leads one to think no one really needs them. They key to talking to them is to understand and be sympathetic to that. It's foreign to them.
But I've had great success talking to them by taking them to a nice, clean, safe place to shoot, showing them my well cared for guns and impeccable range safety habits: I have shown them what the bullets look like and how to load and unload the gun, talked about the different types, and then have let them HIT TARGETS WITH them. They ALL grin after hitting a target with a big handgun. You can show them that it can be very safe to own guns and shoot them, and it's not just something scary people do, it's something normal people do. I'm a somewhat pudgy woman in her upper 30s, not a threat. By the end of the day I've never had anyone tell me they'd still vote for a law that would take my guns away. Not once.
Sometimes, but not always, it leads to discussion about self defense, and with the experience of shooting fresh in their mind, they feel more able to imagine what an empowering feeling it is to know there is a way for any person, large or small, strong or weak, to defend themselves when no one else can.
Some have become gun owners.
I applaud your efforts and am glad you converted a few. As I said for me, these are acquaintences not friends and the only one I broached the subject to of going to the range with me looked so terrified at the prospect I didnt pursue it further.
In my experience, a .22 rifle is the best weapon to introduce someone to firearms with.