How?
What evidence suggest the world is getting better? We've made huge leaps technology-wise and scientifically, but that isn't the point.
How are the morals better than when the last generation were here?
I think a fundamental problem with that question is who defines "better" and what is their definition? While I can see many ways our world is going to hell, I can also see ways we've improved, by my standards. (My loose, very general standard is helping is good, hurting is bad. YMMV)
Consider violence, for example. Let's assume that increased violence, i.e., increased hurting, is bad. Yes, it's true we see more violence on television than we once did. I personally don't care for this. From a historical perspective, however, our acceptance of violence is much lower than the past. We don't publicly feed slaves to lions, for example, or have public battles to the death. We don't even have public executions or dueling, to use examples from our more recent past. So although there is more simulated violence in our lives, there is less actual violence.
Consider also tolerance. As a whole, our tolerance for others is much better than it was a few decades ago. Overt racism was once accepted as normal, and often applauded. Now it is mostly condemned. Similarly, tolerance for alternative sexual preferences is greater than it used to be. Neither is perfect, but both are better. Assuming you believe tolerance is a good thing, television has actually helped improve tolerance.
But I can certainly see other examples where we've become worse rather than better. Overall, I believe we are much greedier and self-absorbed than we once were. Gone is the sense of obligation to one's community, replaced with amorality: if it's good for me, do it, with no consideration of impact on others. Television has definitely encouraged this, with it's focus on consumerism.
Television has also hurt America's intellect, helping to make us more ignorant, and even literally dumber as a whole. Politics is a great example of this, though not the only one. Television has helped replace the involved, well-read, well-informed American with a nation of ignorant couch potatoes, educated by sound bites and dishonest advertising. Of course television is being quickly supplanted in this by YouTube. It's brought a whole new level of ignorance to the next generation.
My $0.02.