I'd worry that it also eliminates the opportunity to have those tremendous back and forth type discussions where people help each other and make incremental improvements to the idea they're working on. That's a lot more rare than two people griping back and forth - but what price would you pay for the sublime?
You would really lose the 'discussion' aspect of things by turning it into a 'say once' system.
People in complex situations almost never behave exactly as you'd expect them to. An artificial limit to discussion might have terrible unintended consequences.
What about the problem of someone asking a question in their comment.
"Hey, wait a second, what did you mean by X?"
[I'm sorry you're prevented from replying in this thread]
This to counter number 1, but I see other issues too:
2. Trolls do not care who replies. This can avoid the argument between the OP and the troll, but does not prevent the latter to post the snarky comment in the first place. Some people just want to express their frustration attacking someone, they do not care about replies. Moreover, the lack of chance for the OP to reply could even incentivize the bad behaviour, giving the flamer a sort of "revenge" weapon. People often find gratification in silencing others.
3. Some discussions give value to the community because they happen in a short lapse of time. If someone needs 2 hours to reply, then there is a chance fewer people will see it.
4. As I said, trolls just want replies, from anyone. Flaming the full community could even be more satisfactory to him.
5. Unfortunately often there is no way of doing this because some users do not have their address in their profile.
You would really lose the 'discussion' aspect of things by turning it into a 'say once' system.
People in complex situations almost never behave exactly as you'd expect them to. An artificial limit to discussion might have terrible unintended consequences. What about the problem of someone asking a question in their comment.
"Hey, wait a second, what did you mean by X?" [I'm sorry you're prevented from replying in this thread]