We were on the plain with DD (2) not long ago. On the way out a co-passenger complimented us on her behavior. I smiled, but smirked inwardly - she had slept the whole flight! Strangers are so bad at judging parenting that their opinion holds no value in my eyes.
Mostly, IHMO, when you judge other parents you are judging struggling people in the middle of a bad situation. I occasionally get whiffs of judgment with DS, who is non-obviously but severely disabled.
This! The random judgement of people who are seeing a snapshot in time means nothing to me. If I see a parent struggling with a tantruming child I never thing, "What a bad parent! She obviously does this, this and this....how dare she inflict her poor parenting on me!" I walk away feeling sympathetic, because I've been there. I've been there soooo many times. My son is six now and mostly well behaved, but it has taken YEARS to get there. I've done five different parenting courses, I've tried every discipline technique under the sun. Spanking has NEVER worked, time outs work sometimes. Removal of privileges works, sometimes. Reasoning with him works, sometimes. As other posters have said, children and not carbon copies. Every child is different, some are easier than others and some are oh, sooooo much harder.
My mother is the most patient person I know. She has raised four, respectful, successful children. She once told me, after I'd rung her in tears, completely at my wits end and feeling like the worst parent in the world, "Love, while I adore my grandchild completely, looking after him on his own is more difficult than taking care of three toddlers at once. You are doing the best you can with an incredibly opinionated, intelligent and stubborn child. Breathe, you'll get through this."
So, when I see a mother standing red faced at the check out, while her toddler writhes on the floor and screams, I think, "I wonder how many times she was woken last night because he/she just wouldn't STAY in bed? I wonder if that child's father ever takes the child and says, "Have a sleep, read a book, visit a friend, I can see you're not coping." And most of all, I know that feeling of red hot, burning embarrassment. The feeling of complete and utter failure and the desire to just sink into the floor, or burst into tears. But you don't, because you have to pay, scoop your child off the floor, wrestle him into the car seat and load the groceries, while people stare, glare and mutter because you MUST be doing something terribly wrong for your child to behave like that. Only children who aren't disciplined throw tantrums, and we should go back to the day when you just got out the wooden spoon when you got home.