I understand being protective. I understand being afraid to let go. I don't think you can protect kids forever and scouting is a great first step.
I think the key to protecting our kids is educating them. Not scaring them. Letting them know that scary people are out there. That people hope that when kids get scared, or made to feel uncomfortable that kids won't tell. That they'll tell kids things like "don't tell", or it's a secret, etc. Tell you child that YOU will always believe him, listen to him, and want him to talk to you NO MATTER WHAT.
Teach your child how to stand up for himself - to bullies, to adults that scare him or make him feel uncomfortable. Teach him how to stay safe - when answering the phone, when the doorbell rings, when he thinks be might be being followed, etc. Teach him how to get away from someone who's grabbed him.
You son will be much better off and better prepared if you teach him these things about life instead of sheltering him.
Go ahead, join scouts. Bring him to every meeting. Get to know the leaders. Carpool and meet his friends. Ask him about his meetings. Stay engaged without being a worried mom.
Best wishes.