Bitcoins will be hard for them to stop without shutting down the entire internet. Should a government act against bitcoin, it would drive the price through the roof.
There are already a few governments which have acted against bitcoin, and how do you think has that helped bitcoin? It is thrown around in the media negatively, residents of a country are thereby even restricted to use it because it is banned in their country now. Also, bitcoins doesn't have such a strong backing by a lot of people that the whole internet will be fighting for them. I don't think the internet or the people care about bitcoin as much as you believe they do.
The legal status of bitcoin is different from one country to another because these rules are changing/being created slowly. While some countries have explicitly allowed its use and trade, others have banned or severely restricted it. Even different governments have classified bitcoins differently, some realize its power and embrace it while some are scared of it. Bangladesh, Bolivia, Ecuador, Russia, Vietnam are some places where it is termed illegal.
Bitcoins are legal in so so many countries also, and if people of these countries are able to use bitcoin for their benefit positively, it will also attract attention of other people. And the government can't stop the people to get from what it wants, because otherwise they will be overthrown by the people. The government gives what people want, so it is more important for people to know bitcoin first, then want it
