Karen, it was not so long ago that there were several national stories in the news with people who decapitated others with swords and long knives--one in a university building, one in full view of others on a bus. Seattle has had several instances of mentally ill persons menacing others with a sword. (Granted, in one case where it looked like the sword wielder was going to do more than that, he was shot.) I have personally been threatened with both edged (including axes, swords, and knives) and projectile weapons (including a bow, but yes, firearms too) doing work with mental health agencies and going on (escorted thank god) child removals (nowadays it seems like the police do a lot of the removals, or so I have heard, I've been out of the workforce for 10 years now). In other areas of the world, I can guaratee you that there have been a few people maimed and/or killed by machete today.
Swords and sword-like weapons are lauded in our culture too, especially as it fuses with others. Lightsabers, ninjas (extremely innacurately portrayed, if I might dump out another pet peeve here), and pirates come to mind. You can even buy Hot Pink Jolly Roger paper plates for your glitter pirate birthday party and pink plastic swords too, for goodness sake.
Are you saying that play is only creative to you if it as a prolonged death scene that involves prolonged self defense before the inevitable? Most play sword fights (including lightsabers) I have seen do involve someone/something dying at the end, generally after many slashes and strikes. The kids might have more time to negotiate, I guess. I'm not really sure my adult mind really is more comfortable with death by sword. Decapitation seems rather painful considering that most people can't do it cleanly, and a piercing wound is immensely painful no matter by what implement. And since you mentioned fencing, you know that from the sport perspective, the results at the higher levels happen in "bang you're dead" speed many times.
The children who playfight gun battles are exploring many of the same themes. If they want to be correct, they probably should recreate a prolonged death scene and self-defense--because guns do not kill people as fast as many people imagine unless it's a very lucky shot, and it's often an agonzing, frightening death. I imagine the people through the ages (up to and including WWII and beyond) who have faced being attacked by swords found the experience frightening and painful as well. In addition, it's often not the death itself is the point of either "gun fights" or "sword fights" (often prettied up to "swordplay," but let's be real here), but the chase (which can also feel really icky to us adults, for understandable reasons).
Again, I support any parent who wishes to restrict whatever play they wish to. It's not silly at all to be concerned about societal and peer influences over your kids when it comes to condoning violence; nor is it silly at all to be very careful about safety.
However, what I DO think is a little silly is romanticization of swords over guns. Look at this this way. Put the most bluntly, rifles and shotguns do and always have had hunting applications. Pistols less so, but you could I suppose. But it is not general practice to run down a deer or a rabbit with a sword or chuck your saber into the air to bring down a goose for dinner. So which one is the one that is "only used for killing?" If having any sporty application removes the "only used for killing" label, then you must remove it from guns as well as swords. I choose to categorize created weapons (vs. anything you pick up can be used as a weapon in some context) as...weapons. What people do with them (collection, sport, hunting/slaughter for food, murder) is another issue. But kids often explore death in their play. So I don't really think of murderous/abuse themed children's play as indication of future problems necessarily--but they are uncomfortable for adults to witness sometimes.