I don't think anyone would contest that good behavior would be good for society. But, it's not a practical expectation, because the probability of everyone exhibiting good behavior is vanishingly small.

That is exactly security through obscurity. If you're relying on people being nice enough to not exploit you (no matter how difficult it is), you have no security at all.

Let's say everyone on HN was nice enough to not use exploits. Might be possible. But then one person does a drive-by exploit, and BAM. Everyone but one person is nice enough to not exploit people.

Just because you wish people were nice doesn't make them nice.

No, it's just lack of security. There's no obscurity involved at all.

(And, if there was any doubt, we should of course not count on people being nice on the internet.)