I dress my son in camoflage as he loves everything army. By not allowing him to dress in anything camoflage I would be inhibiting his way of expressing himself and I think it would be heavy handed of me to impose my views on him like this.
As a treat he is allowed go to the army surplus store and choose child's sized versions of military gear, so he has a helmet, a waistcoat with lots of ammunition pockets and an army water bottle. He loves all of this and will often wear the waistcoat when we go out so erm....you can say camoflage figures big in our lives.
However, I don't like camoflage stuff with slogans and rarely buy them. I also try to avoid dressing ds in camoflage from head to foot and make sure he wears non army outfits as well to balance things out.
I am not too keen on skull imagery either, but don't ban it 100%. I am constantly surprised how much skull and knife imagery crops up on cute 'pirate' clothing for young boys, including the up market, more expensive labels.
I never ever buy clothing with negative messages on them - ie words like 'idiot' 'stupid' 'lazy', Primark is full of this sort of stuff for boys which I find is a great shame.
I also have one strict rule. When we go to church, ds cannot wear anything army. This seems to be a general unspoken rule amongst all parents at our church. I explain to my son that church means peace and forgivemness, so it's not a good place to wear army clothing, even if soldiers are not bad men (which of course they aren't).