What you say is true and applies to ANY commodity market (or in fact any non-centrally regulated market): FX, precious metals, oil, textiles, fruits, etc.
I can set up my own independent exchange to trade, say, gold in the same way there are thousands of online gold exchanges. Then I can artificially inflate the gold prices on my exchange, using fictitious money (like the willy bot did), leading customers to come to me to trade their gold for high prices, and therefore impacting the worldwide market price of gold... at least a tiny little bit for a tiny little while... until customers find out that they can't withdraw their fictitious money from my exchange, so my sham and its impact ends right there. This is what happened to MtGox in February 2014.
The bigger the market you are attacking is, the less time it takes for the sham to be discovered, because the tiny percentage of people who try to benefit from the fictitious high prices quickly overwhelm your ability to fake solvency. A huge market like gold would pretty much suffer no effect due to its size. And as the Bitcoin market continues to grow, the hypothetical impact of such a sham should diminish over time.
I wanted to add that naturally it is very costly to run this sort of attack. Because as you are artificially manipulating the prices, you have to keep paying out the customers' arbitrage profits. This is why willy caused MtGox to lose tens of millions of dollars in the end. Mark Karpeles was simply clueless or naive in thinking willy would help him. So don't do it, or you will lose money :)
In summary, I do believe regulation can and already does help BTC. They bring finance professionals in the market who have a clue (unlike Karpeles). They bring trust. They bring more trading volume. These are all things that make BTC less manipulable, hence less manipulated.
Is there a difference when it comes to Bitcoin that makes it unique? In your example the majority of gold exchanges are regulated, arent they (if not, lets use a stock exchange as an example instead)?
In that situation the bad actor is unregulated, and the others are all regulated. With Bitcoin the opposite is true - only one exchange is regulated. Does this matter?
I can set up my own independent exchange to trade, say, gold in the same way there are thousands of online gold exchanges. Then I can artificially inflate the gold prices on my exchange, using fictitious money (like the willy bot did), leading customers to come to me to trade their gold for high prices, and therefore impacting the worldwide market price of gold... at least a tiny little bit for a tiny little while... until customers find out that they can't withdraw their fictitious money from my exchange, so my sham and its impact ends right there. This is what happened to MtGox in February 2014.
The bigger the market you are attacking is, the less time it takes for the sham to be discovered, because the tiny percentage of people who try to benefit from the fictitious high prices quickly overwhelm your ability to fake solvency. A huge market like gold would pretty much suffer no effect due to its size. And as the Bitcoin market continues to grow, the hypothetical impact of such a sham should diminish over time.