Why do mothers do this?

My little boy and I are in the grocery store, I hear a child crying. I look over in the next aisle, see the toddler in the cart crying and the mother either saying, "you better shut up." or something along the lines. On occasions, I have even seen the mother discipline the child. I have my own beliefs and they are this: I will never discipline my toddler boy in public, I do not believe in this. It is embaring, and brings unnecessary stares. It is not conducive to him nor myself. I would rather discipline in the comfort of our own home. Why didn't the mother try to figure out what the baby wanted instead of telling her to shut up? My son is always content and happy when we go to the grocery store. I always bring his bottle, just in case. If he starts getting antsy, I will talk to him in a loving way, or if we are towards the end of the check out line, I will grab him a bag of doritos, open the bag, give him a chip, and place the bag on the conveyor belt so that i can pay for it. I guess I'm just a wuss when it comes to parenting. What do you think? Do you agree with mothers that do this?