Even though double spending risk at no confirmation is little to none, the risk is still there. People don't understand how Bitcoin works and draw the conclusion that any no confirmation transaction have the risk of double spending. However, it is worth noting that in the event of 51% attack, transactions can be reversed relatively easily. It can be done but lots of computing power is needed to initiate such attacks. Many other methods still exist for transactions with no confirmations, all the seller have to do is to take precautionary measures to ensure the risk is minimal.