Would HN be better if personal insults and death threats were allowed, would it improve the exchange of ideas and the expression of opinions?

Yes. Your idea of a personal insult is my idea of spirited debate. I've been warned twice in the past few weeks by HN moderators because I've used similes that they've found offensive. Honestly? I find that offensive. They'd better censor their censorship.

I'm no stranger to insults, I can take what I can dish, but I also think this is true: everybody can argue their point without being personally insulting (some, like me, take getting hellbanned a bunch of times, others just do it straight away), but not everybody can look past the insults and focus on the points made. So a free-for-all this excludes people who simply don't like being insulted while gaining nothing when it comes to the content of the discussion, the arguments.

FWIW, I'm not a huge fan of downvotes, and I don't even like things being ranked by upvotes. But the rough spirit of focusing on substance and backing up claims, that I like.

I think you will find many people disagreeing with you on that. In Germany it's even illegal to insult people because in Germany dignity is considered to be a human right just as much as freedom of speech is.

Clearly, Germany has failed - If people had any dignity, they wouldn't need a government to protect it.