And herein lies (part of) the problem.
I drink a LOT of water. That said, I cannot stand paying the "Outrageous" prices of Bottled water. Upwards of $3.00 for a 20 ounce bottle (not just at airports though... many other places too.) So I like to bring a bottle of water with me... Oh but wait.... I cannot take it through the security. Instead I have to ditch it and BUY one on the other side. Really?
So how much Sun Screen do I bring? 3 Ounces is NOT enough for a week long trip. Oh, wait... I can buy it at the destination. (usually tourist areas so it's more expensive too.) Then when we leave.... I have to throw the excess away. Same could be said about many other items. (Shampoo, body wash, mouth wash, bug spray, on and on and on...)
It's just more hassle (for me) then it's worth. When I travel alone (like for work) it's much easier. I don't have allergies, and I will use the hotel's soaps/shampoo and the like, but with the family? Not happening. Not to mention that my wife doesn't like to fly anyway.
It is fine, maybe even encouraged, to bring empty bottles through security to be filled at drinking fountains on the other side.