Isn't there a huge risk when you can "cancel" unconfirmed transactions?

A lot of people do not know that you can cancel transactions with -zapwallet for instance, so that the transaction is canceled and the bitcoins are back in your wallet. People might provide goods or whatever before the transaction gets one confirmation.

Don't you think that this is a huge risk? Especially for merchants who don't require confirmations? Or am I missing something here?
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