Most of the people keeping bitcoins as investment think that the value will go high, the more users use bitcoins. This is a demand/offer reasoning and it's based on the fact that the current protocol allows only X bitcoins to be mined.
How likely it would be that a future hard-fork removes this limit or just increases the number of bitcoins in circulation? This would destroy the value of bitcoins already mined.
I would highly doubt for there to be any consensus related to removing the Bitcoin cap. This is for the same reason you mentioned, such a fork would absolutely destroy the value of the coins mined, and any future coins. Luckily, everyone has to agree on it to move, or for such a thing to actually take effect.