Bitcoin supply does grow until 2140. It will inflate only if the backing economy and users does not grow until then. If this growth outpaces the supply of bitcoins, it deflates. And just every economist (and every piece of empirical data we have) will tell you deflation is about the worst thing that can happen to an economy, in terms of monetary events.
Inflationary policies also have a very tight link with speculation in the economy. You only need to look at the past 2 years.