if 1 BTC=US$1, I will buy 210000 BTC (i.e. 1%)
Exactly what the title says.
If bitcoin dropped to the price of a dollar (which we hope it never will), what would you do? Buy more and hold, sell? Buy a promising altcoin like ETH?
I personally would buy more bitcoin.
You are willing to invest $210.000 for bitcoin when it's value drops to $1, without even considering the trend of bitcoin by then?
What if bitcoin is actually dead by that time? You're only going to be investing that much to a dust.