I link to specific articles from MMM, GetRichSlowly, and introduced them to YMOYL. The important thing isn't attacking their ideology, it's showing them that there is another way. My buddy here at work, who is the best case study in this, still owes 17.9k on a 25k car he bought 3 years ago(11.7% interest, due to my insistence he's finally gotten that refinanced down to 5.7%), had a full balance on his CC's for pretty much his entire adult life(only 4k thankfully), ate out all the time, commuted ~50 minutes each way, and didn't have a Costco membership. This was causing marital issues as well. He was ready and open to hear about another way, and he's making excellent progress on all fronts. He's paid off several debts including the CC, moved closer to work, and by the end of '13 he'll have no debt besides the car... if that(it is possible to have that paid off as well).
My parents? My mom just finished up a short sale on her home, she's 48, and has ~40k I think in 401k's. She, however, isn't a spendthrift, she just hasn't been very good at optimizing many things, such as cars. I'm working on her, slowly, but she's also working on me, trying to get me to "live a little" which is advice I could certainly use sometimes.
Bottom line: don't attack them, show them that they don't have to do what they're doing, but don't try too hard on people that don't want it. Another guy at work always leases cars, and will continue to do it into the future. There's no hope for him. I accept that.