I've done a couple of things.
I too was misinformed about car seat safety. My article on flying with children actually forced me to learn and I realized how many mistakes I had made. I live in Europe (no excuse!) but the situation is worse here (fewer rfing seats, higher harnessed, etc.)
I post pictures of my kids as babies with thick jackets on or ffing to young or too loose straps and then point out the error of my ways on my own comments. So in other words, I hold myself up to be the ignorant one while disseminating the necessary information. Of course, some of you don't have a cache of bad-use car seat photos-and good for you!
I'll also try to insert it when they're still pregnant, or just found out they've been matched with a child. "Congratulations! And if you have any questions about car seats, please let me know. I've done a lot of research..."
I do say something when that horrible "We didn't have car seats and we survived..." argument comes up. I will say "That's because those who wouldn't have been here IF they had been in a car seat aren't..." I think we owe it to the little ones lost of our own generation to speak up for them. My mom's reply is a little more tactful. She's a nurse and tells people how they don't have enough child-sized organs for donations anymore because of car seats. "Well that's one disadvantage to using them". Not as many kids being killed in car crashes... Makes the point clear!
ITA on the other parenting issues. My cousin has decided not to vax and my sister is having a fit. I'm all "Please don't say anything!!!!!!" I don't need a family falling-out on FB thank you!