While I can't speak for past generations, I have definitely noticed an extreme decline in parenting... Is it the reason, EVERY TIME, for a child acting up, in public or otherwise? No, kids are kids, and kids will BE kids.
Personal example: My three year old is normally VERY well behaved and has great manners, I have actually been complimented on this.
A few weeks ago, he was just ON ONE. Tired? Maybe. Just in a mood? DEFINITELY. Everything he saw, he informed me he NEEDED, and when I said 'no,' he'd start whining about it. It escalated from there... I was in the party section, shopping for kiddie gifts and he saw a package of motorcycles that he just had to have. O.M.G.
I didn't tell him 'no,' I told him we'd get him a better one when we went to the toy section, IF he was a good boy... He went OFF!
Screaming, crying, yelling at me. If it hadn't been last minute shopping, I would've left. I hoped for the old "out of sight, out mind" magic that is a toddler's mind at times, and it worked... he calmed down when I went to a different section.
Am I a bad parent because my kid acted up ONCE? I'm thinking some people in the store at the time probably would answer "yes." But anyone who knows me, knows it isn't true.
EDIT: I might add, that my son got NOTHING at the store that day. Everything that was in the cart for him already, went BACK. And he didn't get to ride the Mickey Mouse car when we were done.
Momma means BUSINESS.