With gold... what if huge mines are found? or some asteroid once we have advanced technology? that makes me a bit worried for the long term.
I would also rather have people that just bought BTC cheaply because they liked the idea rather than some warlords that stacked tons of gold through centuries.
The 'bitcoin supply limit' argument is not necessarily sound because of A) forks, and B) clones.
In the cryptocurrency industry, the market-shares of BTC and other crypto-assets are threatened by the existence of competitors. Either ones that are similar, exemplified in the case of Bitcoin and it's forks, such as Bitcoin Cash or Bitcoin Gold, or ones that are superior to older iterations that they improved upon. In this context, a limit such as 21M units is not necessarily helpful.
Gold, meanwhile, has no known economical way to be synthesized. It is true that influxes of supply could devalue it at some point in the future, such as deep-earth mining or volume taken from other celestial bodies. But that is a different kind of work and entails different risks than simply creating a competing cryptocurrency.