It's not that you don't receive messages but that you need to keep installed 14 different applications on your phone or get used to 14 different UIs to do the same thing.
The major problem is the WhatsApp vs Telegram split for me, if all my friends were on Telegram I wouldn't really need it.
Self hosted Matrix sounds like a good solution and I'm happy with managing my own server - but the UI quality (Elements) is just not on par with Telegram, so I'm still there.
I agree with you, it's nice to relegate spam to Linkedin / Email, but that can be achieved with marking contacts as friends vs random people and having a unified messaging platform.
For me, my unified workflow is my phone, which I have tuned to receive notifications from various platforms in various different ways (push, pull, manual). Even if I could tune Beeper to do the same, I would prefer not to have to duplicate my effort in setting preferences, which I've already set at the OS level.
If I send someone a text and they receive it in their email inbox because that's their preference, what difference does it make to me as the sender?
Unless you go to the effort to tell people that you route your SMS messages to e-mail and therefore reply in-your-own-time (hours/days/weeks delay), the people trying to contact you aren't going to expect that: they're going to expect you to reply much sooner. I'd be out of a job if my boss' panicked SMS messages about how our prod website is down went to email instead of my phone.
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Any kind of "universal" messaging platform that anyone can use to send anyone a message needs to allow recipients to set how maximially intrusive those messages are - but senders might also want a way to set how minimally intrusive those messages are. Those requirements cannot be easily reconciled in a way that protects privacy and prevents abuse while also allowing anonymous and unsolicited messages or senders. So far the "best" way to do that today is by segregating senders (not recipients) by system (e.g. private SMS for high-intrusive; less-private-but-guarded e-mail for low-intrusive; public social-media, etc).
Consider services that tried to work-around that, such as LinkedIn's paid messaging feature - which didn't exactly go very well.
So long as iMessage is sold as "better SMS" then that's fine, as it inherits SMS's limitations (above) - but it isn't a portable, platform-agnostic, geography-neutral, messaging platform, and I'd rather people didn't try to use it as such.