Too much heated debate will hurt The Monastery, because heated debates tend to eventually devolve into borderline flamewars or even outright flamewars. It might be more accurate to say that having a few "lively" individuals helps make the place more interesting.

Update: And I'm not sure I buy into your "heated debate" theory. The common bond of trying to solve problems with Perl, how open we are to accepting and helping those new to Perl, and the diverse background of various Monks are arguably much more important. I mean, if you, tye, and ikegami never got into a pissing match ever again, I seriously doubt The Monastery would crumble.