There are a few different issues. First, volatility is universally bad for a currency, because it makes all transactions in the currency more risky. Money should always be a medium of exchange first and foremost; there should be little to no room for speculating on the value of money and people should not have to factor in unexpected changes in the value of money when determining prices. In general people will switch from more volatile to less volatile currencies because less volatile currencies make trade more efficient.
Unexpected deflation is particularly bad, because in addition to the general problems with volatility, it also triggers defaults on loans (because money becomes more difficult to obtain). Too many defaults in too short a period of time will create a "contagion" effect by reducing the collateral held by lenders (who use loans as collateral for their own debts), which triggers even more defaults. Worse, as lenders see their collateral vanish, they will try to make up the difference with money, taking money out of circulation and causing even more deflation and thus more defaults. This is the "deflationary spiral" scenario.
Inflation is not some trick to hand money over to "Wall St." Rather, a low, predictable rate of inflation is targeted so that there will be some "breathing room" during an economic crisis. It does not hurt people on a fixed income because it can be planned for and the fixed income can be adjusted for inflation (e.g. someone could hold a portfolio of TIPS). It also has nothing to do with the price of computers, which have become cheaper because of economic growth (and in fact have become cheaper over decades of inflation). Inflation also encourages investment activity by discouraging the hoarding of money, which is a good thing for the economy.
