If it were a question of letting "passionate, smart people have it out", then sure. Unfortunately that's not what you get in practice on the open internet. What you get are (a) people who want to vent their personal issues for whatever reason, and (b) windbags who think themselves smarter than they are.
These can quickly dominate the threads. That repels the smarter people. This is how we could fall into a death spiral. Worse, the risk grows as the site grows, because then more people are attracted to it for wrong reasons. (Right reason: curiosity. Wrong reasons: hearing the sound of one's voice, venting indignation, or making others do so.)
To sustainably have a forum of the kind you describe, you'd need to close it off from the public internet. We're not going to do that with Hacker News, so we rely on guidelines to prevent the worst. This does come at the cost of a certain blandness, leaving the site "a little flat", as you say. But better flat than dead.
These can quickly dominate the threads. That repels the smarter people. This is how we could fall into a death spiral. Worse, the risk grows as the site grows, because then more people are attracted to it for wrong reasons. (Right reason: curiosity. Wrong reasons: hearing the sound of one's voice, venting indignation, or making others do so.)
To sustainably have a forum of the kind you describe, you'd need to close it off from the public internet. We're not going to do that with Hacker News, so we rely on guidelines to prevent the worst. This does come at the cost of a certain blandness, leaving the site "a little flat", as you say. But better flat than dead.