TL/DR: "If Byzantine Fault Tolerance [0] does not create a huge advantage for your use-case, it is unlikely blockchain makes sense to consider over a traditional database."
https://eprint.iacr.org/2014/765.pdf
"Regarding BA, we observe that Nakamoto’s suggestion falls short of solving it, and present a simple alternative which works assuming that the adversary’s hashing power is bounded by 1/3."
One important difference between how a truly BFT system behaves versus Bitcoin is how Bitcoin handles network partitions, or rather, how it doesn't handle them.
Specifically, when Bitcoin goes split-brain, i.e. in the event of a network partition, Bitcoin will "reorg" into two new chains, both of which will happily accept writes from both sides. When the partition is healed, one chain will win, and the writes to the other chain will be clobbered. Ideally these transactions will wind up in the mempool again and be accepted into the new chain, but that isn't a guarantee, more of a band-aid, and doesn't change the fact the system ostensibly acknowledged a write it then lost.
On the CAP triangle, Bitcoin has chosen to sacrifice partition tolerance (i.e. Bitcoin is NOT partition tolerant), and this is bad: https://codahale.com/you-cant-sacrifice-partition-tolerance/
There are ways to turn Bitcoin into a truly BFT system. The main one I like is decoupling proof-of-work from transaction processing, turning it into a leader election system for a more traditional BFT algorithm, such as ByzCoin:
https://arxiv.org/abs/1602.06997
With ByzCoin, if you can't reach quorum, you can't make progress, so in the event of a network partition the system will simply stop accepting writes if it can't reach quorum, as opposed to accepting writes which will go on to be clobbered by a future reorg.
This may be a stupid questions, but how does such a system prevent me from adding new nodes, only to remove them all at once if I want to prevent the system from progressing?
Besides , how many times in history a continental network partition of the internet has happened?
And it would only take a single node connected to both sides (land and satellite?), to undo all the work of the would be attacker.
Continental? No. Country-wide? Many, many times.
Imagine being in Egypt during the Arab Spring revolution when the government shut off Internet access. Imagine selling product to people for Bitcoin, seeing your client software accept the transaction because "enough time has passed", and then a few days/weeks later, when Internet access is restored, seeing your wallet balance get clobbered by the much-longer global chain.
/shudder
This is definitely a band-aid: a good database doesn't lose writes it acknowledged.
What blockchain achieves is proof of history given only the latest block's hash. This might or might not have a PoW on top of it to achieve BFT.
Practical example:
An authoritative server which responds only with the latest block's hash (this is cheap, think microcontroller cheap) is another way to make a blockchain useful with no BFT. This way blockchain distribution can be offloaded to untrusted peers while the actual agreement is not distributed (and thus no DFT is involved).
EDIT:
Off the top of my head I can see a few applications of such an scheme: imagine a very low-power device taking mission-critical measurements. This device would periodically distribute a message consisting of (current block of measurements + previous message's hash) to untrusted high-power-large-storage clients. In case of any client desynchronizing it can request from its peers the measurement chain, and only has to receive the latest message from the low-power device to ensure the chain he got has not been tampered with.
That is not BFT because the source of truth is just an authoritative server. There is no distributed consensus even if there is distributed storage.
Git is not a blockchain (it's a DAG) but that misses the point: I think the term could perfectly be retrofitted if it was the case. Things predating a term don't invalidate the new term convering them.
Either way I disagree with your opinion and there's nothing to argue further that would change either of our minds.
Sure, the powers of the world that want to engage in financial censorship probably don't think of unstoppable transactions as benefit.
But the people that oppose censorship certainly do think of it as a benefit.