The fixed supply doesn't really make sense if you want BTC to function as a unit of exchange (rather than a commodity). I won't go in to the reasons why since they have been elaborated on by many other people.
However, the fixed supply does incentivize holders (ahem hodlers) to increase the value of the coin - whether that is by starting companies that use BTC, spamming HN with BTC/Reddit related posts, etc. It's an interesting way of arranging a bunch of people in a sort of distributed boiler room.
That said, once the mining subsidy completely ends (assuming BTC is still actively used then) its possible we will see some calls to increase the supply. Otherwise the transaction fees will need to become huge (or the price will need to rise 1-2 orders of magnitude) to support current levels of mining activity.
