This statement is ridiculous. The opposite is true, bitcoin needs liquidity, which is provided by traders.
Please explain why it need liquidity if people are using it as a currency? Do you need liquidity for your current fiat currency? I'm sure if you are from the US you're not going man if it wasn't for all the day traders this five dollar bill wouldn't be worth the paper it's printed on! Oh wait, it's not..... Because of all the people on Wall Street making bets they can't pay when they lose sending our economy and the global economy in the shithole. If you spent/saved what you earned and there was slow steady growth why would you need liquidity? Why would you want your savings to be in the hands of day traders and 20-30% swings? If you managed to save 100 Bitcoins and they were worth $1,000 each and you were retiring from your job and needed to cash out would you want to open your account and see that your savings just went from $100,000 to $70,000 or worse $50,000? No. That's why slow steady growth and a flourishing economy where BTC is functional and used to earn, buy, sell etc is the best thing for its long term growth. If you want to bounce it around like a penny stock then it will be dead in a matter of a year and some new and improved coin will come along and the big boys will toss it around for awhile until they've made their millions and toss it aside like an old toy the kids don't want anymore.
Bitcoin is an idea to change the world economy as we know it. Take back control of our finances and out of the hands of greedy corporations and politicians. But everyone is so god damned worried about lining their pockets with fiat instead.
Until you can easily live fully by just using BTC, there needs to be an easy way to convert BTC<->fiat. Right now, in almost every place, people still have to buy food with fiat, pay for their fuel with fiat, pay the rent with fiat, get paid for their labour with... you guessed it... fiat.
In the ideal future, where a fully self-contained Bitcoin econonmy has been established, there's no need to keep liquidity in the BTC-fiat pair, but we're far away from that. And isolating BTC from fiat right now isn't the answer either, because that will practically nullify any attempts of getting the currency accepted by many more merchants and consumers.
I'm not saying isolate it by any means. I am saying stabilize it. Forget about making fiat off of BTC. Buy it, use it, save it, or cash it out if you need too. This can easily be done by buying and selling OTC instead of on the exchanges where a single power player can ultimately tank the price by filling buy orders all the way down to $20, and when that happens every other site follows suit. Mt.Gox and big BTC holders have way to much power over the price. How do we limit this? How do we take the fluctuation out of their hands and put it back into the everyday bitcoiners hands? Like I said slow steady Bitcoin growth and price is the only way we survive.
The bolded actions require liquidity. If you want stability, convince the whales to cash out, distribute their coins, and get it over with. Until then, liquidity is necessary for everyday purchases of BTC to spend, save, hoard, whatever.