monozygote I don't see "the" problem
I assure you that my position is not a religious belief and it's not security theatre.
I will try to make a better example and put some explanation on it, but please, try to not read this post as a "me vs you" argument.
Let's try again with Keepass and see how it goes.
If you encrypt your disk, you are achieving a very specific security measure, that is preventing people to read your files from your (post-mortem or powered-off) device.
When you power on your device and input your encryption password (or a password to access the encryption key), everything is unencrypted to the live system.
This means that a malware running on your system will read clear text data.
This is the reason why, having another layer of encryption is beneficial (And specifically why a keepass file is encrypted in the first place).
If I have to make another example, we could talk about encrypted password on a database, preventing admins (or hackers) to read them.
Next step (continuing with the keepass example) is that even if your hdd is encrypted, and even if your keepass is encrypted, you have another layer of protection, which is keeping passwords (and some variables) censored.
The reason you have this other feature is because you are preventing another set of attacks (shoulder-surfing, remote screencast, etc.).
monozygote Disk path Isolation/sandboxing/access-control provided by Android (and storage scopes isolation on top of that by GOS) is sufficient IMO
Why Disk lisolation/sandboxing might be not enough? Because you might have that part of isolated disk infected, or the sandbox broken.
I wouldn't trust Vanadium sandboxing to protect my keepass file, that's why I encrypt my keepass file.
All of this to specify that on every step you might have different attack vectors that needs different solutions.
monozygote Your firewall argument is similarly a flawed comparison. [. . .]
monozygote What's that got to do with the process memory protection offered by the OS to different apps running on that OS on the same system?
The firewall example:
Don't think about your laptop.
Imagine a Border Router, followed by your corporate firewall, followed by your web-server, followed by the firewall, followed by your back-end server (maybe sql server).
On every step you are applying network filters (ACLs on the routers, Policies/Rules on the firewall and Policies/Rules on the servers).
My point is that even if they might implement the same rule (Let's say TCP/443 ALLOW), they are not doing the same thing.
They are all necessary because they are protecting you from different sets of attacks and attack vectors.
This is true not only because they are different layers of your networks and have different software running, but also because they do the "same" job in different ways.
An ACL is less powerful than a netfilter/pf rule which is less powerfull than a firewall rule (Especially if you have Application Control on it).
The point I am trying to make is: you need protection on more layers.
I agree that Router and Server and Firewall are different machines, the analogy is that also inside the same system (Let's say your OS), you have the same issue: processes/services/software might get affected by different processes/services/software. This is why you should consider to have more than one line of defense.
monozygote If db encryption was that big a thing it would have happened already (assuming it's not the case just now)
eggy If it was strictly better, the Signal team would have already integrated its features.
The reason it is not "strictly" better is because this specific layer of protection has some trade-offs that Signal is not willing to include in the user experience.
If we have to examine this feature from a pure security perspective, this feature is "strictly" better (and Signal itself had this feature in the past).
If we have to take into account also user experience, I agree that this is not for everyone, and that's why you have Signal and Molly available to install.
I hope this gives a better insight on what I meant to communicate, but really, I would understand if you think this logic is incorrect: everyone has different objective and opinions and this is perfectly fine.