Yeah, at least Lemmy tries to warn users not to use the DMs to send sensitive or private information, and suggests using a dedicated encrypted messenger instead:
The developers are very busy developing lemmy-specific features and encrypted DMs would be a lot of work to create something that is a bit redundant. But I am sure that if someone would want to make that, they would appreciate that help.
Not that I particularly trusted reddit, but at least it was 1 corporation with (hopefully) some solid security procedures in place, and potential penalties for data breaches. Whereas in Lemmy, it might just be 2 random guys.
Personally I wouldn't trust 2,000 random guys any more than 2 random guys. I assume any of my unencrypted communications are public.