Site owners can make their own rules, it's their 'business' and if theft was an issue it might cause their customers to go elsewhere. my local site has banned projectile grenades for H&S reasons, which doesn't seem to be an issue, if theft was prevelant at any business I attended then I wouldn't feel my property was safe to be left unattended & I would take measured to protect it, mud sticks and this thread kinda proves it in my eyes.
Opinions are like arseholes... everyone has one.
Mine is, I'm in favour of a ban if it's warranted, I'm not a site owner so my opinion only affects me.