Cartoons are doing just fine right now.
The thing is, when people think of cartoons from the 80's, 90's, and even the early 00's, they tend to lean towards remembering the good stuff. And the highs of these periods are VERY high.
But lest we forget how wretchedly low the lows were, as well. There were PLENTY of cartoons from our youth that were nothing less than garbage. It's just that most of us don't remember them, or remember them through rose-tinted nostalgia goggles.
You want examples? Look no further than MovieBob's Big Picture episode on video game cartoons. And that's just one aspect of how bad cartoons used to be.
So when people say that new cartoons suck, and old ones are better, I can just point to Captain Planet and go, "Really?".
(PS, I am not saying all old cartoons were bad, by any means. I'm just saying that it's important not to judge an entire generation of cartoons based on solely the good stuff)