Seriously, it's a slippery slope. "Nothing of substance" is a term that needs more clarification that what that post provides. It seems to suggest that if the criticism is too harsh, then it's no longer substantial. I think there's a better guideline than that.
The best ideas not only can withstand criticism, they get better with criticism. If you examine what's being revealed about Apple and Steve Jobs -- the most successful company in the world right now -- it's not that they avoided criticism. And contrary to rumors it's not that they didn't nurture seemingly "dumb" ideas. Jobs would toss them out there all the time, by his own admission. Nurturing crazy young creative ideas and rigorous critical analysis are both part of Apple's process.
Apple's secret is that the criticism is directed at the idea not the person. That is what defines "nothing of substance": the target of the criticism, not the intensity. If it's about the idea, that's substantial, even if it's harsh. If it becomes personal, then that's truly not adding substance.
You "throw it in the cauldron" and then rigorously debate everything in the pot in a manner divorced from the people who contributed it. That's how you boil it down to the best stuff, not by holding back.