Swarming is the girls' natural way of starting new colonies and they are genetically programed to do it. While there are lots of techniques that can interrupt the process, there are times you just can't stop mother nature. I am not too keen on the idea that if your hives swarm you are a bad beekeeper.
And I strongly second Scott's opinion that it is not a good idea to destroy queen cells. Put'em in a nuc to bank'em if you can, but like he said, if you destroy them and the girls swarm anyway you could be in a world of hurt, or at least be out the $$ to buy a new queen when you realize the old one left with the swarm.