That exposes the entire Bitcoin system to the artistry of every pump-and-dump team that operates at MtGox.
It's great for the professional speculators, but it's not good for the system as a whole.
However, given the usual human herd mentality this idiotic situation persists.
Serves everyone right who continue to perpetuate the trading centralization around MtGox. So, party on!
You are completely misinformed about this. MtGox has actually been losing centralization since 2011. It used to comprise about 85% of the market, now it's probably around 60%
But even if everything centralized at MtGox, that still doesn't mean that price would become more volatile. It might indeed mean less volatility, because one larger market means greater liquidity and a smoother trading experience with lower spreads.
There's also nothing wrong with people gathering to one exchange for their trades. It is not efficient to have a million exchanges. Some degree of centralization is market-efficient and we should let the market make that determination (which it's doing).