The fact is we all get judged by others no matter how we behave with our children.
I was in Asda when DS was 3. He asked for chocolate and I told him no, he'd already had chocolate today. Cue crying, wailing, moaning .. I did what I thought was right. Went down to his level, told him calmly that he was not having more chocolate and that he could have a fruit snack. He continued to cry so I continued to shop with him walking beside me in tears ignorning his behaviour (he was crying because he wasn't getting his own way).
Lady approaches me and it goes like this
Her "Is that your son?"
Me "Yes" (surprised)
Her "You might want to try being a mother to him"
Me 
Her "I've been watching you shopping and ignoring his cries. Poor wee lad"
Me 
Her "tut-tut" and a lot of headshaking
Me 
Point is anything I did would have been wrong. If I'd shouted, I'd have been wrong, if I'd given in and bought him chocolate I'd have been wrong, if I'd mollycoddled him for having a tantrum I'd have been wrong, I ignored his bad behaviour and I was wrong.
I am not a shouty mum personally, I find firm voice and consequences for misbehaviour more effective.
I don't think it's "normal" to shout at kids all the time but nor should we rush to judge a parent because you've seen one or two incidents.
If you believe a child is in genuine danger/abuse/neglect/desparately unhappy in their family life then I'd be the first to make the call to social services.
But unless you know more about a family, you cannot make a rash judgement on a few minutes that you've witnessed.