Why do I think altcoins are valid? Because the financial industry wants to hedge security, and one, single block chain does not give them that. What if Gavin or some other guy issued an update that imploded the BTC network? They're just supposed to accept 100% loss? No, they're not going to do that.
This argument is part of the Alt-coin Narrative Cycle. It is only considered valid by people who don't fully understand how bitcoin works. As people learn more about bitcoin, they will learn that it is not possible to "implode" bitcoin by an "update." Even a network split event due to a poorly-excuted forking change wouldn't result in anywhere near a 100% loss. It would be annoying, some double spends would occur, speculators would no doubt dump coins, but things would return to normal.
How is it possible to "implode" bitcoin if the value of bitcoin is stored in the blockchain ledger?