Also Signal requires a phone number to sign-in. It's not exactly private. AFAIK the proprietary server can glean your IP, your phone number, who you talk to, and when you talk to them. This type of metadata is valuable information.
The WhatsApp co-founder gave Signal $105M in 2018. Signal costs ~$50M/year to run. It's also funded by wealthy donors such as Jack Dorsey (Twitter, BlueSky, Square). BTW Jack is now pushing Signal to integrate Bitcoin.
When evaluating the "ethics" of a chat platform, we should factor-in the metadata, soft power, and eventual leverage that centralized (controlled by a few) platforms like BlueSky and Signal afford to wealthy folks who are bankrolling it.