This comes up pretty often, but it's worth noting that it's built-in scarcity. Deflation in the sense of increasing purchasing power will only happen if it is more widely adopted as a medium of exchange (which is definitely possible.) It its use as a medium of exchange diminishes, it could actually see inflation in the sense of decreasing purchasing power.
Unlike cash and gold, Bitcoin can be divided down to 8 decimals. So it doesn't really matter how many millions of bitcoins there are. The important thing is that bitcoin can't be printed by central banks.
Children don't like their parents forcing them to eat vegetables but that doesn't mean it isn't good for them. You may not like the bank controlling the money supply but that doesn't mean you haven't benefited from it.
And my claim is hardly "baseless". You can reject the orthodox views but please don't claim to be in the majority -- whether we use the polite term "heterodox" or the less polite "crank" the fringe nature of such views is apparent.