It's not that they are stupid (though they may be, I dunno) it's that they have to answer to their bosses for anything they let through that proves to be problematic, and they, like you (and me) will err to the side of caution. They would rather block something that would be OK than let something through that isn't. It's pointless to get angry at them, and at any rate it's not an argument that you can win.
lol, but just saying -you're giving the definition of incompetent as opposed to stupid. Stupid would refer to them being of low intelligence unable to make decisions whether work or non work related. You're just saying they are incompetent at their jobs since they aren't able to make correct decisions since what can or cannot be accepted is a black and white issue, they could err on the side of caution because they are incompetent or they could be competent and just make correct decisions. So they aren't stupid they are just incompetent then.