The problem is that your (and the OP's) social circles have changed, and you haven't sought out new ones. For some reason, you expected [x], as it existed at [time y], to stay the way it was, for all time.
Change happens. Expecting otherwise is foolish in the extreme. What is around you has changed, and has changed you, and you haven't sought out something better, so you blame your surroundings.
You went to YC Demo Day - why didn't you go somewhere else? Why did you wait for them to come to you, at an extremely famous conference no less? If you want to re-experience the good old days, find the ones who share your ideals - you had to do that in the past. That's how YC started (I'm idealizing it, to serve as an example - I don't know the facts). People didn't simply show up and beg to do something good the day PG was born, they had to be found, the culture had to be grown, until it grew into the behemoth it is now and started attracting all kinds.
Your surroundings have changed, why haven't you changed your surroundings? You had to do that to get to the good old days, why aren't you still? Or did you simply coast into a seemingly-ideal world, and are now forgetting / ignoring that your colleagues (and slightly earlier) essentially created the dot-com boom? Were their intentions really so pure?
If the culture you entered into is what you wanted, but you don't want to do the work necessary to continually re-create it, why are you surprised that you can't find it now? Think about all the time and effort that went into creating it prior to your entry - if you aren't exerting similar effort, why are you blaming others that it changed? If the YC-of-old is what you want, why are you going to the YC-of-now, and not working to create what you want? That kind of risk and effort went into creating it in the first place, if people aren't willing to do so it will not happen.
And that has not changed. And more people than ever are putting in that effort, by sheer virtue of an increase in raw quantity. That you have drifted away from that world doesn't mean it doesn't exist.
What I am talking about is what I perceive to be the mindset of a great many young people entering the working world today. This has nothing to do with where I hang out (indeed, I avoid stuff like that, actively!) YC Demo Day, I went to because I didn't have the full picture of what it was like. Now that I know, I have not gone back.