Friends and family cannot cope when I set 7 day message timers on Whastapp, Signal and SimpleX.
But when I tell them how would they like it if all their in-person conversations were recorded indefinitely, they suddenly get me.
Online messaging should be off the record BY DEFAULT.
And more often than not, people scrolling chat history more than 7 days, often don't have the best intentions and are out to get you.
Eh, there are pluses and minuses to deleting messages.
For me personally, having tons of ancient, many years old, emails and other messages with Isis Lovecruft and others saved my ass when she falsely accused me of rape. And I would have been even better off if I had more.
...and yes, in court she never even tried to contest the validity of any of the non-digitally-signed messages. Claiming stuff was faked is an uphill battle. Especially against the guy who created OpenTimestamps...
I get the desire here, but disappearing messages really just add a level of inconvenience without doing much to increase security. No matter how secure the system, one can always take screenshots, or worst case take a picture of the screen. (And for personal relationships as you describe, the difference between a signed message and a screenshot is going to be slim to nil.)
It's just a good practice, works against 99% of people who never bother to take a screenshot.
If it's such an inconvenience, make it 1 month instead of 7 days. But if you need that much permanence, you need to start to question if email would not be the best medium for that specific conversion.
