You're talking about an improvement on gold, not fiat. Controlling the money supply is a useful property of fiat, a tool not available with Bitcoin.
TL;DR: Deflation is not "a good thing." See http://en.wikipedia.org/wiki/Deflation
At this point, Bitcoin's inflation rate is way higher than USD--that's what mined coin is. Bitcoin supply will continue to inflate throughout our lifetime.
As was pointed out by Satoshi, the price of Bitcoin tends to the cost of mining it (and vice versa). In other words, the price of producing one bitcoin tends to the cost of producing it. This means that if Bitcoin ever becomes substantially more valuable, the value dumped into mining it will proportionally increase. Do you think that ~10% of the world's wealth is going into maintaining today's fiat "ledger" every year?
controlling the money supply is just a nice way of saying the banks get to print money and loan it with interest, it is not a useful property, it is a fraud and theft.
deflation is not good? do you like paying high prices? technology improves productivity all the time why is it bad that prices come down, would you be happy if cellphones still cost the same as a car?
Bitcoin's monetary inflation rate is higher than USD's but the amount of goods and services sold for bitcoin grows much faster than the inflation rate and so purchasing power increases.
you are ignoring the fact that the mining reward is halved every 4 years, even if bitcoin doubles its value every 4 years the miners still get the same purchasing power (because they get less bitcoins)