Its anonymity is its own worst enemy.
If global governments discover that criminals or terrorists are using bitcoin to fund their activities — and at present there are very few checks and balances in place to weed out this sort of behavior — it could prompt a crackdown. If governments around the world instituted regulations that made it difficult to own bitcoin, we could see prices plunge.
It's response to this was that...
Yes, this is entirely possible. As I’ve talked about many times before, governments hate any form of currency that they can’t track, control, and tax. They hate cash and they hate cryptocurrencies even more. It’s entirely possible that some governments will make bitcoin illegal, though it’s just as likely that they’ll do what Japan did, and just surrender to it because so many people are using it.
Regardless, let’s say your government made bitcoin illegal. So what? Marijuana is illegal in most countries. Does that mean people don’t use it? Does that mean the price of marijuana is low?
Hell no! Indeed, many years ago, before marijuana became legal in my state, I strongly considered being a distributor. This was because I was seeing guys make as much as $4000 per day supplying this stuff. The fact that it was illegal drove the price up, not down.
So, if bitcoin becomes illegal in your country (which is a big “if”), you’ll still be able to buy it, and it’s value might actually go up.
I personally think that governments will eventually be forced to accept the concept of cryptocurrencies the same way the US government has had to accept both marijuana and guns; there’s just too many people owning and using these things for them to ever be made illegal in any practical way. Bitcoin (or some other crypto like Ethereum) will be the same.