You'd be surprised.
Is there an article about the huge benefit of for-profit journals? How abortion is an affront to God? How ISIS is trying to do some good in an area?
Are you really suggesting there's really no bias towards certain demographics or viewpoints?
There's a definite demographic that posts here, and it is very much an echo chamber.
My claim is that you (I don't mean you personally, but all of us in your position) perceive HN as an 'echo chamber' on such issues precisely because it isn't. I imagine there are small biases on some of them, but people exaggerate this into "groupthink", "bubble", "echo chamber", etc., not because that's how it is but because that's how it feels.
This is by "design". These are almost the only things that are on-topic here and we mostly like it this way. I'm sure you know.
No one's suggesting that, but the fact that you had to pick those odd examples to make your point is evidence that on many common issues (which I hesitate to name because even naming them makes sparks fly) this community is deeply divided. And when people complain about HN being biased against their view, it isn't ISIS or abortion they're thinking of.