What Global crackdown?
Most governments already accepted Bitcoin either as a currency or a commodity

In any way, if governments decides to "ban" Crypto currencies, people will just go underground with it.
They cannot stop the Bitcoin network, because it is decentralized and nodes are spread all over the world.

True.
Completely agree.
But still, if the government takes major action against BTC or crypto then it might be dump hard as people from all over the World remove their interest. So ultimately it will impact on price., which is the most volatile characteristic of Bitcoin. And finally, collapse.