Pickledsiblings - you need to look at the school. I've taught in "special measures" sink comprehensives where the GCSE pass rate is 16% and the aim is to keep the pupils in the room - if they learn something then it's a bonus and I've taught in "Ofstead Outstanding" schools where the discipline has been so strict the children don't dare breathe without permission.
The two are completely different animals. As a teacher, you have to assess the class and work with your pupils accordingly. You asked if teachers had ever allowed the behaviours you describe - I said yes and told you why.
To be quite frank, I am not going to give a bottom set year 11 girl in a sink comprehensive a row for eating or drinking in class or texting, when I know that she's spent the night on her best friends floor because her step father beat up her mother (again) and she hasn't had breakfast. Nor am I going to pick a battle with a 16 year old boy (ex-child soldier from the Congo) who has just sworn under his breath because he's starting to get annoyed because the teacher in the previous lesson didn't tell off the boy who called him an "asylum seeking scrounger" and started to push his buttons to wind him up. I'm going to settle them down, treat them like adults and give them an hour a week away from their crappy lives by making my lessons somewhere they can rescue their battered self esteem - even if that's just completing the tiniest bit of work.
I am going to (and do) come down hard on the child who is taking the piss because "they think they can get away with it".
Teaching is NOT black and white. Sometimes the home lives of the pupils are so completely chaotic, school is just an extension of that chaos and pupils act out because they are seeking attention and negative attention is better than no attention. Sometimes, it is frustrating and hard and yes, you do want to kill the little shits because (yet again) another lesson has gone to ruin through poor behaviour and they haven't learned anything, but as a teacher you deal with it in the best way you can.
I wouldn't want my child in the school I describe - I make no bones or apologies about it, we will be going independent when we educate our children because we can afford it and I consider that the local independent school to us is far superior to the local schools, BUT, that doesn't mean the teachers in the "difficult" or local schools are crap. They have different issues to deal with and often a teacher is 4/10 social worker, 4/10 mentor and 2/10 teacher.