There's more of everything now, and it's all more accessible, so naturally there's more crappy art. There's more good art as well, if people stop whining about what their television places in front of them and go find it.
It's always been the case that if you just allow the media to spoonfeed you your entertainment, you'll end up with the blandest most universally inoffensive nonsense available. Mainstream media is about pleasing as many people as possible with the same product. For every Pink Floyd, there's ten Bay City Rollers.
This. It's like reading the comments underneath a YouTube video. For every legitimate, intelligent post, there are 30 posts saying "this video is gay" and "tHis SUXXXXX!!!!!1."
Culture hasn't declined. Stupid people just have a much easier time being heard.
And yeah, maybe the internet has made it easier for random "mediocre" people to get their 15 minutes of fame, but it's ultimately fleeting. People might remember the Double Rainbow video, but does anybody remember the guy's name?
On the flip side, the internet has also made it easier for truly talented people to get themselves out there. Instead of hoping to meet the right people at the right time, they can get their work out to a much larger audience without needing to be "discovered."