The attacks in bitcoin are mostly headed in to the argument that bitcoin has no value. Though there are a lot of argument to throw, I will share some point to invalidate their argument. Because it's really invalid.
In the field of economics, it says that, there are characteristic to determine if an object has value.
First, scarcity, if X (E.g. Bitcoin) has LIMITED supply then MAYBE it has value. Same in the nature of gold, gas and other minerals, one of the reason why its very expensive and it's getting more expensive as the time pass because it has limited supply.
If you read it carefully I use the word "maybe" because scarcity dont mean value, It's a factor that affects the value. If X is scarce but it has no use or not needed, it wont matter. X must have viable use, that would lead us to the second principle of economics.
The "intrinsic value" can we use bitcoin? will it ease our life? Does it have a viable use? Guest what? Its a YES! With bitcoin we can send money around the world, fast and secure without any intermediary. Directly! Anytime! anywhere! online.
Without bitcoin or other crypto those characteristic of money that is present in bitcoin (e.g divisible into millidecimal, fast, secure etc) is imposible to find on FIAT! Stop on that. IT'S IMPOSSIBLE! Tell them.
To sum up, according to the principle of economics, to know if X has value it must posses some characteristics which is
1. Scarcity
2. Intrinsic value
Does bitcoin had those kind of characteristics? Yes! Its scarce and has intrinsic value. So according to economics, BITCOIN HAS VALUE! Tell it to them, then leave.
If you find this valueable dont forget to merit me! Yaaay!