Well, since a clone is really just a delayed twin, I don't see how destroying clones could be considered anything but murder. If one can ever reduce the totality of a human to data, which can be replicated, morality as we know it will become null and void. (That being said, the expressions of the new morality may not be very different.) Basically, this would do more for popular philosophy than Deep Thought in Hitchhiker's Guide to the Galaxy.

This is one of those questions it is fun to argue, particularly if representatives from various religions can get in on the fun.