The two topics are different.
The Fairphone 2 has an open bootloader (for good reasons, giving the user the key to easily install alternative recoveries like TWRP and all those alternative OSes we like so much on the Fairphone 2).
Anybody who somehow gets possession of your phone can flash or boot anything (regardless of your screen lock or any other security measure when booting is finished) … to then do anything with everything in Internal Storage … your data.
How do you block this possible access to your data?
You encrypt it.
Now anybody can still flash or boot anything, but there’s no access to the user’s data … to use the phone, the data partition can only be formatted, and then the user’s data is gone … no access.
Of course you have a point that encryption users should think about how much of their data goes to Google, Facebook and the likes, but it is not the same matter.