I went to boarding school at 16 because I absolutely hated being at home with my mother. We had an appalling dynamic that didn't really sort itself out until I had been away from home for seven or eight years. I think I would have done better going away a few years earlier to be honest. My mother was in most ways a good mum, and as an adult I can understand why our dynamics were so iffy. But spending lots of time with your parents is not always a happy and good thing. I was bullied at junior school, and my sister at her grammar school, and my parents were totally oblivious, so being at home is no certain protection in any case.
I know lots of people who have been to boarding school, and I have never heard any of them tell awful stories, at least no more awful than the many people I know who have been to day schools (private or not). A couple were sent to very unsuitable schools where they were unhappy, but it should have been completely obvious to their parents that that was going to be the case, as they were pretty unhappy children in the first place, and needed a very different environment (there is a huge variation in the ethos of different schools).
My experience of boarding school at sixth form was that I actually had a lot less freedom than I would have had at home (like having to be back in at 10.30pm every night, for example), but a huge amount more opportunity to do a variety of fun things (like rowing, woodwork, philosophy, organizing a major theatrical event etc). Thinking about the children I was at school with, they seemed pretty similar to the kids I had been at day school with, except they were mostly boys (and therefore silly at times) instead of the all girl environment I had before. Teachers seemed fairly similar too, some odd ones, some brilliant, and mostly in the middle.
One of my relatives is currently at boarding school (weekly) and it has, I think, been a lifesaver for him. He is valued for who he is, and has relaxed in a way that he never had before, and is doing very well academically. His family were in an area that didn't value geekiness, and he was struggling (he is also dyslexic). His mother has another role where frequent, unplanned moves are involved, and where choice is not possible (she is a vicar). His parents really struggled with the decision to send him away to school, they would have preferred to have him at home, but had to recognise that it was not the best option for him. He is quite difficult kid, but has a very close relationship with his parents. It doesn't seem to have radically changed since he went to school.
When choosing a boarding school of course you have to be even more careful than choosing a day school, but there are lots of good schools with caring staff. Personally I hope that I wouldn't have to send my children away, but if I did I would make sure they went somewhere where they would have a great time, with lots of opportunities to do different things that they couldn't do if they were at home (my brother for example took up canoe racing and rock climbing, not your usual inner London sports).