You are not unreasonable if you want to change scout groups for any reason you like. If you feel that this group is not the one for your child, then it's your right to try somewhere else, if you can find a space.
However, it does sound like an overreaction on your part to me, especially as you say your DS loves the group he's at.
The volunteering - unusual I think for leaders to turn down help, but it genuinely could be that they have enough leaders at the moment, and don't need parents to stay. As others have correctly said, if you are staying for more than the occasional week, then you would need to be DBS's anyway. If you are offering to help now and again, they may just not need this kind of help at the moment. I'm a cub leader, we have six leaders in my pack, and don't often need help - if we do, I put a message out to parents and ask. If a parent offers who is a bit of a helicopter parent, I may not accept their offer of help, as it is usually to the detriment of their child to have their parent there. You say you will accompany your child on all day trips - you may not get the choice with this one!
The campsite - meh, a burnt out van and stocks, while a little odd, are not sinister. As long as the leaders are aware of them, and have made them out-of-bounds, and enforce this, then I don't think this is a big deal. There are almost always places on scout campsites that beavers shouldn't go near - woodpiles, barbed wire, workshops, activity equipment etc. Scout campsites are generally a bit more rough and ready than your typical Caravan Club site.
The head scout leader - I reckon every scout group has an older, slightly more old-school leader, who will make a bigger, louder fuss about things like uniform. He didn't handle it particularly well, he's probably used to dealing with teenagers who should be able to sort their own scarves etc, rather than 6 year olds, but it's not unusual to ask for necker to be re-rolled ahead of parade, and for badges to be put on correctly. We, as cub leaders, usually have to re-roll at least half the neckers before parade, although we don't make a song and dance about it.
Ultimately it's up to you, do you trust the leaders to keep your child safe? Do they enjoy it? If the answer to either of these is no, then move your child, or withdraw them from scouting. But don't do it because you find some of the things the leaders do to be irritating, or they piss you off. They're just people at the end of the day, and just because they do things differently to how you would, doesn't mean they're necessarily wrong.