Brian from Backblaze here, glad to answer any questions. To
clarify, Backblaze produces four different products/modes for
different customers with different needs and requirements.
We want customers to choose what is appropriate for them.
One size does not fit all:

1) Online Backup ($5/month) where every file is encrypted
on your laptop BEFORE being sent to Backblaze and your backup
is secured by your username/password - where you can recover
your password if you have access to your email account. (We
support two-factor auth which provides an additional optional
layer of protection.)

2) Online Backup ($5/month) where every file is encrypted on
your laptop BEFORE being sent to Backblaze and your backup is
secured by your username/password AND your private encryption key
is secured by a "passphrase" that is not recoverable in any way,
shape, or form. (Two-factor auth is also optional here.)

3) B2 Object storage (half of 1 cent/GByte/month) where you
store your file completely unencrypted, and this can be "private"
(only accessible by username/password) or "totally public
accessible by knowing the URL". A good application of this is
serving up a web page to the public - you really WANT people to
see all the contents!

4) B2 Object storage (half of 1 cent/GByte/month) where Backblaze has zero knowledge. You cannot browse your file hierarchy because Backblaze doesn't know your filenames. You cannot preview your images. You cannot recover your passwords. There is no other option other than downloading the encrypted blobs and applying whatever decryption algorithm you decided on (we have no ability to know what that is).

Ok, so I think some (many?) people in the security field think that Backblaze should ONLY offer mode #4 (and maybe #3 to serve up public websites). I happen to disagree and I personally feel that products #1 and #2 are useful and appropriate for some customers. But everybody is welcome to their opinion and we want to be completely open as to what exactly is occurring and what we are offering as a service.

Personally I think #2 is an excellent trade off of security vs convenience. Your data is as impervious to attack as a zero knowledge system in #4 for years upon years. Then one day your laptop is stolen or crashes and you want your files back. You want all 4 TBytes back - so you order one of our free (encrypted) USB hard drives to be FedEx'ed to your home with all your data. To kick this process off FOR THE FIRST TIME EVER you tell us your passphrase (up until this very moment it really has been zero knowledge). At this moment you are opening a window of SLIGHTLY lowered security that slams shut after a few hours. For those few hours of preparing your 4 TByte restore, if an undetected hacker had compromised the one restore server in the Backblaze data center that your job was on, that hacker could possibly get access to your files. But then the reduced security window slams shut, we NEVER write your passphrase to any disk so it has now vaporized and we do not remember it, and if a hacker hacks into our system the following day you are STILL completely impervious.

But again, as long as you fully understand the implications of #3 I am COMPLETELY supportive if you instead choose #4 which is our "Zero Knowledge" offering.