Keep in mind that most people who are quick to judge have probably never had to contend with venomous snakes. 
From one who has, a few thoughts on what I've learned, suggestions and a bit of general rambling, hopefully some of which you will find useful.
First of all, in response to the suggestion that you acquire tongs and attempt to relocate a potentially venomous snake yourself: I STRONGLY advise against this and I cannot stress this enough. No offense intended here but whoever suggested this has obviously never been bitten by a venomous snake... While a cottonmouth bite wont kill, it will cause untold realms of pain and possibly problems that may well last for years. Many of the people I've spoken with who were experienced in handling venomous snakes admitted to having made a mistake at some point which resulted in them being bitten. Definitely NOT something someone inexperienced should attempt. If you are certain that the snake is not of a venomous species, then by all means, feel free to relocate it if you choose to, or preferably, leave it to go its own way.
Killing venomous snakes with shovels is extremely dangerous and should not be attempted. If you are close enough to a venomous snake to kill it with a shovel, you are probably within striking range. Most venomous snake bites occur while trying to kill a snake or trying pick one up.
If you encounter a snake you think may be venomous, quietly remove children and animals from the area and, if at all possible, leave the snake to head off on his own. If the snake has taken up residence in your garage, etc., again, remove children and animals from the area then call your local Police department or Animal Control and ask them to send someone out to remove it for you.
Some venomous snake species are territorial, particularly during breeding season, cottonmouths among them. If they're in it, its THEIR territory. If you're in it, you're intruding. Never harass the snake, either by trying to kill it or in an attempt to chase it away as chances are the opposite will occur and you have forced a confrontation. When a snake is encountered, the best bet is always to back away quietly and leave the area.
Never, ever, stick your hand anywhere you cant see. Not under porches, not under missing planks in outbuilding floors, hollow tree trunks, the list is endless. Firmly educate children on this lesson in particular until it becomes second nature as this is how kids are often bitten.
Educating your children is your best option to protecting them. Something to consider... You wrote: "Bottom line ... if a snake gets in my house, and I'm not 100% sure it's harmless, it's going to get whacked." I can relate to this more that you will ever know BUT if "whacked" means by the sharp end of a shovel, its asking for trouble. Remember, kids learn by example... Suppose one day your child decides to kill a snake themselves and that snake actually is a cottonmouth... The old rule of thump: "If you're close enough to kill it with a shovel, you're close enough to be bitten." Something to think about.
In your favor: Venomous snakes need their venom in order to eat. Therefore, they expend their venom very sparingly. Venomous snake bites on humans or animals may be either 'dry bites' (a bite with no envenomation) or bites with only a partial envenomation. Venomous snakes (at least those native to the US) are highly unlikely to 'unload' on a defensive bite.
Do keep in mind though, the more agitated a snake is, the more venom it may expend. This is just my opinion of course but why risk it unnecessarily?
The key to co-inhabitation is to avoid confrontations whenever and wherever possible. The yard should be kept mowed at all times. Never allow it to become over grown. Remove any brush piles, woodpiles, overgrowth and anything else that may offer hiding spots for snakes. (You probably already know this.)
If encounters become frequent, you may want to consider erecting snake fences. There are several theories regarding snake fencing, some work better than others. Some may be more effective in certain regions than in others. My snake fences were constructed of wood planks with two strands of hotwire, one at the top and another on the outside and set at least a few inches into the ground. The idea is the snake attempts to climb over, touches the hotwire then heads back in the other direction. Optimal height, materials and so forth, for an effective snake fence varies from one person's opinion to another's. Personally, I consider it an investment, I opted for a minimum of 24". 3ft along the border of the property where the snakes occurred most frequently. If you try snake fences, whatever method you decide on, the fence charger must be of a 'weedburner' verity, especially if your property borders land that is overgrown.
Lastly: continue your quest for education of the snakes in your area. Learn as much as you can about them, which I know you are doing. Don't be put off by the unrealistic opinions of a few, its easy to criticize when its someone else...
I am quite fond of snakes myself... Obviously! =] I hold no grudge toward cottonmouths or any other though having been bitten. It was my mistake. I prefer a live and let live policy, but, should a confrontation be unavoidable, I'll do what needs doing. (Not with a shovel! )
Hopefully some of this well help, if there is anything else I can add, let me know.
And next time I'll call animal control if I'm not sure exactly what has moved into my home.
