Actually they can if all major ISP's work with governments. They can detect the protocol and ban miners who don't follow the rules. Hell, governments could quite easily take over (or nationalize) all mining in the best interests of the nations or for national security if they wanted to.
Now, imagine gobal governance and a cashless society where every transaction is logged forever, and every bitcoin/crypto address needs to be registered, else transactions are dropped. Every police station in the world is connected to INTERPOL database. It would be simple - but time consuming - to implement a Bitcoin or Crypto Address Registration / Transaction Approval Service database every major ISP is connected to.
Have you seen what's happening with filesharing? It's not that easy, countries who try to shutdown Bitcoin entirely will likely end up bankrupting themselves trying to catch everyone who breaks the rules.
Yes, I am seeing illegal file sharing sites and services close up shop, relocate to, and reopen in more accommodating jurisdictions. Those jurisdictions are becoming fewer and far between. What happens in the future if/when those jurisdiction completely disappear?
BitTorrents are often filtered by ISP's. I believe it would be possible to allow certain torrents through based on the hashed values of the torrent/content. Legitimate torrent/content providers could register their torrents/content.
I believe in looking to the future and planning for it. Do you really believe that the worlds aristocracy will allow Bitcoin to jeopardize their control of society, politics, and governance and the finance that controls them without using everything at their disposal to combat, destroy, or control it?
I believe they will attempt to take Bitcoin and make it their own, or replace it and their own inferior technologies with "their own" superior blockchain technology. We are already seeing the assimilation and controls being set up in business, finance and governance. These aristocratic families and corporations - that have the legal rights to legal tender/money creation and distribution - have been ruling the world for centuries or more. We have yet to see their best efforts to combat Bitcoin. We called all this years ago. The question is, will the People win when 99.8% don't even use Bitcoin? Will the people even allow themselves to win? The overwhelming vast majority of people go right along with media and government, and the financiers and aristocrats that control them.
I am a realist, but have high hopes for Bitcoin.
That said, the last 5 years has been interesting, and so should the next 5.
OH please shut up , just ask thoose chineese that have a GFW that they penatradte every day
blocking bitcoin will not work and wil never work if they try.
http://onemileatatime.boardingarea.com/2015/05/11/internet-in-china-staying-connected-while-traveling/
I'll be a happy man if you are proven right and I am proven wrong in the future.