My question is: isn't bitcoin supposed to be used as currency and not be stockpiled? How do this cope with the fact that its value will hopefully increase over time?
Simple! People need to eat, drink, pay bills, pay for gas, wear clothes, live in a house...... ect. Not to mention all their wants..
As you can see, there will always be consumption.
What you don't want however is rampant consumption and zero savings like we have now, where everyone over consumes and lives beyond their means and is piling on a huge mountain of debt only because they'd be a fool if they saved under the current monetary policy.
And on top of that the scary monster deflation is only a problem when it's the monetary kind which is sudden and unexpected. What Bitcoin will have however is first monetary inflation and then neither monetary inflation nor monetary deflation. Constant price deflation which people can plan for on the other hand, will not be a problem at all.
It's so frustrating that nearly everyone has been brainwashed and indoctrinated in public schools and through mainstream media where they just don't understand that monetary deflation != price deflation.