Mt.Gox is not the blockchain. It is good for Bitcoin if people remove their coins from exchanges. It is only bad for speculators. The counter-party risk inherent in current exchanges does not in any way detract from the value of Bitcoin or the Bitcoin blockchain, which is quite secure.
Let's say everyone removes their coins from exchanges, in fact let's remove exchanges from the example altogether, what is the up and down side?
1) all new crypto becomes forever unheard of.
2) all cryptocurrencies including btc no longer have 'common' market values, presently there is the bitstamp value, the coinbase value, the btc-e value, and you have various values on localbitcoin. without the exchanges then there are literally thousands of values (none right and none wrong)
3) so now with all of the different values who will get into the business of dealing with btc? if it has no stability or reliability or standard how do you set your prices
4) why would you buy any more than you actually need for immediate use?
5) if you only buy what you immediately need, and the quantity of new btc is always increasing, it will result in oversupply of btc
The only reason btc scaled to where it is now is because of the exchanges, if they are removed or can't be trusted to operate properly, the whole btc community suffers.
The answer isn't "NO EXCHANGES", instead it's "MORE GOOD EXCHANGES".