Can we please stop considering this as sword vs. gun? No one here is suggesting that Link's sword get replaced, merely that the addition of a gun into the game or world (as an item, as an enemy attack, etc.) would not damage the series. If anyone suggested to replace the sword and have a gun as the main weapon, I'd be against it to.
But no one is arguing that!
Guns do seem more complex, and violent, in comparison to guns which is likely what ZH is trying to argue for. Having guns in a Zelda game theoretically would cause it to be more violent, which would then be able to compare Zelda to other games which are notorious - Call of Duty among others. Also, we've never had a gun (excluding cannons) in a Zelda game so far, why start now when we could still (ab)use the current features of 1:1 item usage [not saying there is such thing, but it could be possible in the Wii U]? Those could be ZH's arguments that he just didn't word correctly.
Big Octo already covered this but... A gun's advantages over a bow are largely a matter of efficiency and the power with which the projectile is propelled. It does more
damage (in real life), but it doesn't create any more or less horrific of an injury. A bullet is smooth and pierces, while an arrow is rough and slices, rips and tears, much like a sword does. And
unlike a sword
or a gun, arrows stick into their target. How about bombs? Burned tissue, bleeding, loss of flesh... a bomb is arguably far more violent. Or how about the Ball & Chain, which would cause horrific blunt trauma, including broken bones and organs and massive internal bleeding. Hell, to be completely honest, if you got hit by the Ball & Chain you'd be lucky if you didn't just break entirely.
There is nothing about a gun that adds more violence to the series than all, because the series doesn't have gore, and isn't going to be adding it. Nothing will change.
And I don't think many people are arguing that a gun NEEDS to be added. I'm not, anyway. I'm just saying that it would do no harm. As for "Why start now", it's simply because a gun is not a significant change. It's not really anything new, other than it being a new item. And the series is always adding new items. It's the equivalent of having the Skull Hammer in The Wind Waker. It does the same thing as the Hammer, just like the gun would do the same thing as the bow (or at least the same thing as the Slingshot in Skyward Sword), it just looks different.