The 7 year old boys that I know play like this and always have. Back in the day it was Army men. (Vietnam was going on).Toy guns,
Cowboys and Indians (Gunsmoke, High Chaparral and the Big Valley)
Characters were shot and killed all of the time on those shows, but we knew it was just TV.
I recall when our daughter was 3 and there was something crazy on an animated show, I asked her "is this real? This thing on the TV?"
She looked at me with a pitiful face and said, "No Mom, this is just a cartoon on TV" Ha!
You can protect your son, you can search for a group or proper children and families, but you will not always be with him , so he needs to learn tools on how to play, how to fit in and how to exclude himself if he does not like what is going on around him.
You are the one that needs to guide him with this, not just shield him.
There are too many great kids and families to expect to assume that they do not live up to your standard.
Our daughter was friends with some kids, that there was no way before children I would have ever considered I would be daily friends with these people. Granola moms, Hard core Conservative mom, that does not drink, did not understand the Catholic faith and thinks the best moms stay home and care for their husbands and children.
But here I am with some of my very best friends, because our daughter played with their kids and I learned to love and respect these moms.
And sure there were some kids that were just plain mean or completely in lala land, But our daughter learned how to handle those situations. Not always gracefully.. But she learned that some people are just not a good match for her. And she is not a great match for others either.