I say this an an obvious snake lover, but really an overall animal lover and a lover of nature. There is no reason to kill any animal in a natural environment. I live in, and grew up in, Florida, camping, canoeing, wandering through woods and bayous, regularly. I think you may have a bit of an exaggerated view on the cottonmouths, but I do understand. They are the only native US snake that is truly aggressive on occasion.
The thing you have to realize with almost all snake species is, to them, you are a huge, dangerous, potential predator. And they have all evolved various defensive strategies. The key with cottonmouths, is to leave them alone, lol. Back away very slowly, and they will go away. For whatever reasons, they have evolved to stand their ground against almost all predators, which is unusual with snakes. If you can get out of their line of sight (And range of heat sensing, as they are pit vipers), they will try to get away from you as well. As long as there is any movement, they consider "threatening", they can continue this behavior.
As far as breeding is concerned, they don't really have "dens". They are ovoviviparous, meaning they give birth to live young, so the process takes much longer than with most species that are oviparous (egg laying), and the females are very vulnerable during this whole time. Which combined with the natural instinct to stand their ground, can make the whole thing worse.
I would have to say though, from what it sounds like, unless you completely strip your property, and most of the area around it, you are always going to have them. And I would bet you have more than you've ever seen. You can think your seeing the same ones, but these animals can move pretty good distances. I've found them miles from any water source in pine flats in FL. While they do love water, they can be just as comfortable on dry land for extended periods.
