I recently read a William Blum report that included this quote:
"When plunder becomes a way of life for a group of men living in society, they create for themselves, in the course of time, a legal system that authorizes it and a moral code that glorifies it."
Frederic Bastiat, (1801-1850) French economist, statesman, and author*
I see some links with arguments made about the arms trade; it may not be nice, but it's authorised as legal by the government. As Liam Fox said, there is no need to be embarrassed about selling arms.
It may not be an answer to the original question, but it is telling that at about eight and a half minutes through this ELAAF video a spokesperson for DSEi says: "We have a 100% legitimate defence exhibition that we hold in association with the UK MOD....and the reason that I sleep well at night is because we do have a legitimate show, if it went undercover and was backdoor hand guns and rifles..."
It may be legal, but CAAT argue that "THIS IS NOT OK" and along with others are urging us to take action to stop the arms fair and stop arming repressive regimes. This weekend has already seen protestors confronting a battleship en route to DSEi and there are plenty more activities planned.
I spent yesterday over my sewing machine making this to take along with us on Tuesday. Maybe we will see you there! 
