a malicious entity does not need to buy enough mining power to get 51%. they only need enough to continuously suppress the price and push it down gradually forcing out other miners, getting back some of the money invested and also raising their percentage of hashing power as other miners drop out. it would be a slow process and costly but not even close to impossible.
If this attack happened than we would just switch the Bitcoin algo to an Asic resistant algo
https://blog.ethereum.org/2014/01/15/slasher-a-punitive-proof-of-stake-algorithm/ or a Hybrind PoW /PoS algo.
governments learnt their lesson about decentralised networks when file sharing effectively took down the music and film industry. why would they let a threat grow to the point that it could actually challenge them. if i were them i would invest the "pennies" to protect the pounds. and it would take fewer pennies now than in 5 years time.
Well they have never waited this long in the past. What is taking them so long? Bitcoin reached almost a 14 billion dollar market cap and is now valued over 5 billion. Liberty dollar was raided when a little over 7 million was backing up the currency. At its peak Liberty reserve processed 1.4 billion annually in transactions and Bitcoin has volume traded at an average of 60 million usd daily or 22-30 Billion projected annually.
Perhaps those that do understand the threat also understand that attacking a decentralized network is futile as it will just grow more resistant. How are the most powerful countries/corporations worldwide handling bit-torrent thus far? Do you think that they will ever succeed in preventing these transactions or are you suggesting they aren't interested in shutting down thepiratebay and other torrent trackers?
Those "pennies" invested by governments would only slow Bitcoin and evolve it into something much stronger and resistant.