They need to look at numbers and not take facts out of their asses. If Bitcoin is not a good store of value then how come all people who bought before Winter of 2017 have more than they had in terms of real value?
If you bought a car in 2013-17 with your fiat and someone else bought Bitcoin that other guy can now buy 10 or more of similar new cars. To me that's an obvious case of growth and that's more than I need from a store of value.
Maybe some people say that Bitcoin is not a good store of value because it contradicts the definition. A store of value simple refers to an asset that has a market value is not depreciating or decreasing over time such as Gold. Bitcoin's market value is volatile, or changing from time to time; including backdrops in its market price which makes it risky to some people, despite of the fact that its market value is increasing for a long run especially in the previous years.
To make it clear, it is now a new form of investment, because storing fiat to crypto or Bitcoin perhaps, most of the time, is to earn profit over time given that its market value is increasing in the long run.
Currently, still in the earliest phase, bitcoin is used by a few people and with some whales that can make good and bad weather. This is why it is still speculative. In a few years we will be here to talk about it instead as "Internet's Native Money" and then everything will be much clearer.
There will be more years to come for sure before that day would come when Bitcoin is used by most of the people, and I think it is when its market value is stable.