The worry people generally have about these sorts of systems isn't that they distrust the substrate NOW, as you say all bets are off at that point unless you're a cryptography expert and programmer yourself, but rather that they want protection of the data they produce now from being read in the future.
Basically, If twitter wanted to read my data today, they could do so. If they decided in 2 years to read my data now, it would be too late because it was encrypted. With the encryption key, that's trivial. If they have to save the plain text, well that's too late now.
The worry people generally have about these sorts of systems isn't that they distrust the substrate NOW, as you say all bets are off at that point unless you're a cryptography expert and programmer yourself, but rather that they want protection of the data they produce now from being read in the future.
Basically, If twitter wanted to read my data today, they could do so. If they decided in 2 years to read my data now, it would be too late because it was encrypted. With the encryption key, that's trivial. If they have to save the plain text, well that's too late now.