In a global economy of some 64 trillion, 42 billion (plus the gold and other precious metals, and many other "lack of faith" stores of wealth) is not even a drop in the bucket.
And even at that, you don't have to have no faith in established currencies to also use bitcoin. I personally don't think the banking system in power now will fail any time soon, but I also can recognize how valuable a cryptocurrency would be to replace it.
'Objective amount'? What it is is an amount, and growing, that feel exactly what you imply doesn't exist. There are clearly many people that have lost 'faith' in fiat currencies, or the central banks that manage them, or the economies behind them, or all of these things, to the tune of the market-cap of bitcoin. How more objective an amount can you get than that?
Clearly reality is not agreeing with this assessment? As an example of this counter-argumemt : bitcoin.