If your surrounding is this bad then create a friendly environment inside your house for your kids. It is better to have no friends than to have some bad ones. Teach them about respect and patience till they grow up. Parents could become the ultimate teacher of a child.
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I don't agree with that. The best bet is to have 'friends' which are a cross-section of society in my opinion. I've certainly learned some of the most valuable lessons in life from my 'bad' friends, and as a consequence am able to cope in a diversity of societies and social structures. Cloistering, in my observation, leads to viewing society through rose-colored glasses and/or viewing 'bad people' in mostly invalid ways due to lack of background experiences which make it impossible to comprehend necessary nuances.
But you are risking your kid's future here. They are kids not grown men. Kids easily get influenced by people surrounding them or at least try to be like them. The lessons you are talking about will come in the way of their life but spending too much time with some bad character could change their character too. You can not be with your kid all the time till they become a grown man.
That's why I wouldn't consider public schools at this point. If my kids learn how to make a quick-n-dirty pot pipe out of a soda can like I did, that's no big deal to me. If they learn all about butt-sex, genital mutilation, and dangerous drugs such as hormone blockers from some creepy tranny satanist, it is a big deal.