I was privately educated because it was the right environment for me. 12 years in a small, friendly girls school and then two years boarding at a public school. The two years at the end especially were fantastic and I'm so grateful for them.
It's not a privileged bubble. There was a real social mix at my girls school and again at my boarding school; people were there on hefty music scholarships for example. My parents scrimped and paid my boarding school fees in instalments. My friends now are a real mix.
I was a straight A student although I didn't go to schools that hot housed or made rigid academia their mission statement. I found uni harder though, (I did the wrong degree, in all honesty) and I don't have the most stellar job now. My parents, when I asked, said that they don't consider the money wasted at all because education is never a waste, I was in the right environment for me to do well and I was happy. Plenty of people I went to school with have average jobs now, but they're happy and they seemed happy at school. I understand the confidence thing, too. I'm not especially confident in some ways, but I am in others and it often fools people. It's just a comfort zone, I think.
Private schools aren't perfect though. There were naughty kids who didn't want to be there and acted out and my public school had a druggie set. We knew who sold pills, who sold weed and who could get coke, but plenty of us didn't touch them. It's just called being a teenager. Ampleforth school is also famously druggy. Also, to the poster mentioning dick pics earlier, my school had a revenge porn incident before revenge porn was a thing. It can happen anywhere.
People on here who say that unless you go to one of 5 public schools, social contacts aren't a thing have too simplistic an understanding of social nuance though, I'd say. I've seen it in action and I am fairly well connected through school, uni and a hobby I have that I got into through that world (not polo) and being at home in that world is a social advantage. I do alright, I suppose. DP went to an okay comp and an okay uni, did much better than me at uni and has a better job. He's polished himself up on the way, too and is a good networker. But I am the person who taught him to pronounce certain words properly and he experienced London members clubs through me first. Silly examples but they've been of help to him professionally.