That deflation is dangerous is a myth perpetrated by the banking cartel. People have short term needs, like food, housing, and utilities. They will continue to buy those things regardless of whether inflation is +2% or -2% (i.e. deflation). Investors with a clue adjust nominal returns to "real" returns after inflation. Deflation just means they make that adjustment the other way. They still demand a certain real return for a given risk level, so the nominal return will adjust to get it.
Bitcoin represents around 0.025% of world currencies on an M1 basis, and an even smaller fraction of all tradable assets. Nobody bases their economy on it, so the deflation argument is moot. It's just another commodity with a variable value, but one well suited to be electronically traded.
If bitcoin ever became a significant fraction of world trade, you can be sure that competing financial interests would set up their own versions, and then the total units in circulation would not be limited any more. There are already at least 478 such "altcoins" (http://coinmarketcap.com/), but most have trivial value because they were set up by one or two people as a hobby. A serious one would be set up by existing financial exchanges or a government, and backed by a pool of assets to give it stability.