Before I agreed to my son boarding, I spoke to a lot of people who were ex boarders at that particular school - and I only heard good things.
Then I spoke to other parents, and heard about some kids that were struggling, and what was being done to help them, and only heard good things.
Which obviously concerned me, so I did a lot more googling, spoke to teachers and support staff at the school who I found through friends/other parents, spoke to yet more people, and still, heard nothing of significant concern.
The education and educational support my son is getting at his boarding school couldn't be replicated in any other local school - class-size, SEN support, attention from teachers etc. and he missed out on a day place, so we worked with what we had, and TBH, I think it's the best choice for our family.
I think boarders also forget that they don't have the experience of a non-boarding secondary - of the morning rush to get all the books you need ready for the commute and carrying it, with instrument, coat, PE kit etc., trying to do your homework alone at the kitchen table, spending another hour at the other end of the day getting home with all your books, and the impact that has on your relationship with your family too, because perhaps it's not just you on the bus/train getting home, but actually your parent coming to get you, and having to bring younger siblings with them who resent it. How lonely it can be when you're in a large school and don't fit in, whether that's boarding or not.
It's not as simple as boarding is always bad - sometimes the alternatives are worse.