You've been voted down but there is actually a school of thought that excess use of antibacterials and generally going "overboard" (whatever that means exactly) with preventing children from being exposed to natural flora can potentially result in weakened immune systems. There's a lot of pseudo-science in these claims but that doesn't mean there's absolutely no truth to them. It would probably be hard to do a study though and it's not clear who would fund such a thing.
Ignoring the snark (of the parent comment), I've often wondered why it was bad to use anti-bacterial soap (and antibiotics in general), but not regular soap, since both leave some amount of bacteria behind, which presumably have genetics making them more resistant to the pressure. I think part of the answer is that its just not possible to evolve resistance to any amount of soap and hand washing, unlike resistance to the targeted mechanisms of an antibacterial compound.
I'll take a stab at this - I'm an infectious disease epidemiologist that works on hospital infections mostly.
The thing with anti-bacterial soaps is not that the use of the soap is bad. The problem is the anti-bacterial part. It puts amounts of a broad spectrum antibiotic into the environment (be it your hands, your countertop, or the water system) in concentrations that aren't enough to do much, but are enough to put a little bit of selective pressure on the organisms and promote resistance.
It's also not particularly effective - soap and water, through a combination of both mechanical action and how soap disrupts cell membranes, works swimmingly. So there's a cost, and no benefit.
The answer to 'why isn't there a resistance to soap' is that soap, as a chemical, is absurd overkill. It's hellish on lipids of all sorts (tough on grease...and lipid cell membranes), and there's nothing to evolve a resistance to. Not expressing a particular protein, or expressing an enzyme that does a number on an antibiotic compound is effective - to evolve a resistance to soap, you'd somehow have to develop an entirely new type of compound to build cell membranes out of.
And while evolution is rather magnificent, that's asking a little much.
Bacteria evolving to secrete a soap-resistant compound doesn't sound far-fetched at all. Such compounds clearly exist already (e.g. pigments that don't wash off).
Thinking about this more, I suspect there already has been some selection in this direction, but that it has little to no public health impact, as this defense is not useful in places where infections are typically a problem. Indeed, our body is teeming with bacteria (mainly in the guy) that are in fact beneficial, and they've presumably managed some resistance to shear stress and extreme chemical environments (e.g. high acid).
I dated a heatlh care professional for a while who was pretty adament that it was causing detrimental effects in the same manner as antibacterial soap.
That one is...a little trickier. There is some evidence that it works for controlling bacterial growth leading to gingivitis - suggesting there may be some utility for it. But its ubiquity in consumer products makes me a little skittish.
So I don't know if I'd want it gone from toothpaste, but I'd like to see it gone from the many products where its useless or nearly useless, but included so someone can put 'Antibacterial' on the label.
It obviously is possible to evolve resistance to soap and hand washing: It doesn't kill us.
But the gap from a bacteria to something that can withstand the physical barrage of a thorough wash is huge in comparison to the relatively tiny changes to overcome some antibiotics. E.g. an antibiotic might disrupt a single process of the bacteria that is beneficial (for them) but that have a multitude of similar alternatives that are different enough for the antibiotic to fail. Compare that to even just being able to strongly enough attach to the skin to not be flushed away by sheer force from a wash.
There are many reasons that tends to be given for being careful about stronger measures: 1) it is not necessary. It's a matter of being cautious - by using the least effective means that is effective enough, we exert the minimum pressure necessary, leaving us with a larger arsenal of (to us) gentle alternatives to step up to. 2) the stronger methods, the more we kill off beneficial or neutral bacteria too, and by doing so we may make conditions better for bacteria that are nasty for us if we happen to pick them up.
3) we reduce our immune systems exposure to relatively harmless amounts of bacteria and some believe this may be sufficient to actually reduce our overall immune defence.
As DanBC pointed out in response to one of my other comments, there's also the issue of physical damage. While we can bring the heavy artillery and effectively kill anything that lives on our skin, we can as collateral damage cause damage to our skin that creates additional places to hide - effectively a worse variation of washing away good/neutral baceteria - not only may we be removing the competition, but we may be opening cracks and folds that'll be excellent hiding places.
