If you can't teach your kids about boundaries without hitting them (sorry, spanking) then you are doing something wrong. If you have to escalate to hitting it's mostly because you haven't been paying attention before that point, and thats your fault. If my kids did that at WDW, I would only have to look at them and they would stop, because I did the groundwork years ago. In fact, it would never occur to them to do that, and it isn't because I have been hitting them. Hitting is taking the easy way out because it is much easier to do that then to read a book, learn some parenting techniques that work, and then use them even when it is inconvenient for you.
Parenting is hard work, and I actually think - by and large - people are getting better at it.
Here's why I think this: When my mum was a parent, she was completely alone. She had no friends with children, so she had no one to ask if she was doing things right, if I was "normal", if everything was going to be okay. Her only book was Dr. Spock, and I evidently hadn't read it. As a result, she spent most of her time parenting from a place of panic. Taking a belt to my butt didn't do a darn thing to make me any better behaved.
When my kids came along, there were so many more books available to me and - even better! - I could turn to parenting boards on the internet for help. I could talk to experienced parents and bounce ideas off them. I put a heck of a lot of study into learning how to parent my kids. I was so much luckier and better supported than my mom. And, as a result, my kids were better behaved and I could choose not to spank.
These days, we generally only have one or two children, and they're often very carefully planned for. Kids aren't always an inevitable (and often unwanted) consequence of two people getting together. Which means - collectively - fewer of us take them for granted, and we spend more effort on learning how to parent.
Which doesn't mean there aren't still badly behaved kids at Disney, and parents who don't know how to parent.
But I'm sure they're no more common now than they were in the past, and there might even be fewer of them.
My favourite Disney bad-parenting moment... Tired child is lying on the ground in line at the bus stop, whining. Mom leans down and smacks him. "Stop whining!" The child immediately rears up and smacks her right back, on the leg. Then flops down and starts whining again. Mom pauses, and you can actually see her contemplating infanticide. Then, evidently realizing that she can't beat the child to death in public, and being unwilling to give up her spot in line, she simply stares blankly off into the distance, ignoring him until the bus comes.
Poor exhausted mum... it would have helped if she had something other than hitting left in her parenting toolbox.