Car seat controversy

Long post sorry

My kids are 10, 9 and 6. The older two are still in backless boosters, and 6 yr old in a harness. I am constantly being told by family, friends and some strangers that my oldest two shouldn't be in boosters and I'm sick of hearing about it.

The law in my state says they don't have to be in a car seat after 8, but it's recommended to keep them in one until 4'9". I'm going by the recommendation not law. My youngest is in the harness because my middle seat doesn't have a should belt, so no booster can go there.

My questions are why do ppl think I'm wrong for them being in car seats? How old/big were your kids when you quit using one and why? How do I nicely deal with these ppl who have a problem without flying off the handle again?