The first, the number of BTC in circulation is very low 5.6 million or so, which makes markets very illiquid and extremely volatile. Even if all 21.6 million were in circulation, and completely fractionalized- (140 years from now?) the volatility would still be hard to deal with and build a stable economy upon. Yes it may go up against the USD 100% in a day, but it can just as easily go down 75% in one day, depending on what the large old holders do.
How many total bitcoins will be in circulation if the BTC is fully fractionalized?
Don't let the decimal point fool you... it's arbitrary. There are actually (to use your number) 560,000,000,000,000 btc units in circulation now (each btc has eight decimal places). I think the real number is more like 6.5m btc right now fyi.
It's true the market is extremely volatile right now, but it's because A) we're in a period of wild speculation and adoption and B) not that many actors are involved yet. Volatility will necessarily smooth as the market cap grows.