Hopefully the OP is still keeping up with this thread; it is a couple weeks old.
That said, I agree that "converting" them is only going to happen if they want it to. If they're happy with an extra titanium mug just in case, and all the rest of it, then no amount of "Seriously, guys; just try my cat can stove!" is going to work.
However, every single time my dad goes backpacking, he swears he's going to get his pack weight down. He certainly favors the traditional heavyweight style with a splash of bushcraft rather than UL, but this past summer I got his pack weight to 20 lbs for two nights. That was really good; I see room for improvement of course, but he was completely satisfied. And that's what matters.
The watershed moment for him, and for me as well, was looking at it not from a weight/technique angle, but philosophy. Like Skurka says, are they/you/am I out there to camp, or to hike? Personally, I'm there to hike. I was hiking till dark even when I carried 40 lbs for a weekend. Now I can do the same thing, but be comfortable all day because I'm carrying 15 lbs total. I mostly use camp to eat and sleep. I try to keep a journal on each trip, but before I'd usually fall asleep in my 5 lbs tent with my pen in my hand. Now I finish and go to sleep much more normally. Or stay up and watch the stars!
So if they're unhappy with their huge weights, then talk about why they go backpacking in the first place: for the camping, or for the hiking? If it's for the camping, then who cares when it's only 5 to 10 miles to a beautiful basecamp? And if the camping is it, then just enjoy the easy hikes and your friends' company. And go get big miles on solo trips.