Some years ago I responded to a horrific accident in a convenience store parking lot. A dutiful mom who didn't want to leave her child for the 3 minutes it would have taken to pay for her gas took him out of the car, into the blowing snow and toward the store. They wer crushed under a semi she didn't see because she was carrying the child through inclement weather.
Sometimes, the safer option is, in fact, to leave the child in the car if paying at the pump (for example) isn't an option.
Maybe if you live in nice moderate climates it's safer to take the child every time, but where I live, it's much safer in a hailstorm, in a blizzard, in really miserable weather, to leave my child safely in the car for those few moments.
If it's simply a matter of convenience, I'm all for takng the child- kids don't come programmed to be easy and convenient, but sometimes you have to use your judgement as a parent to make the safest choice for your child. I live in a town of about 350 people. If someone calls the Sheriff to complain that I've left my child in the car while paying for gas in the middle of a snowstorm, fine; I'll have a chat with the Sheriff, and go on about my life with no further annoyance. He might wonder why someone was such a busybody, but such is life.
Certainly, I'd make different choices if I lived in a different area, but I have to live based on where I live, and what I feel is best and safest.