I agree with Cornette somewhat, but most of the problems he's blamed on ECW (like saying it desensitized people so much that it now takes almost three or four chair shots to get even half the reaction that one chair shot used to get) would have ended up happening anyway.
It's an example of the business (and things in general) changing and evolving, not always for the better. It's just like movies - they're as violent as they've ever been. In fact, people laugh at films that are a lot older because everything back then (if you go far back enough) looks so tamed compared to the amount of violence and gore that they're used to seeing now. It's just like sex in movies too, where back then, seeing a woman half naked could get a shocked response from the audience. Now look at what you see. It works the same way in wrestling - things that used to be more of a rarity are gonna end up being used in a much more abundant quality. It's almost unavoidable as time goes on, although ECW definitely helped speed up the process.
As for ECW, it never would have lasted with the type of product they put out. Like Vince said on the Rise And Fall Of ECW DVD, you can do the hardcore and more physical stuff on an off/on basis but doing it every night and being what the entire product advertises and presents is gonna catch up to you. Unless ECW evolved into a normal wrestling product over time, I don't believe for a second that they would still be around today, even if Paul Heyman had all the financial backing in the world back then. Even then, it helps to remember they appealed to a small, niche part of the audience. They could have never competed with WWE once the company went public either, because going public was largely done as the best way to compete with a media giant like Ted Turner, who owned WCW.
You can't deny the impact though, which is even more telling considering they didn't exactly have the advertisement and global reach that WWE and WCW did, who traveled the country and the world to get the audience they did, and also had several generations of history behind them, whereas ECW came and went in under a decade.