I'm fine with people not finding me automatically. If Signal wants to keep the low-resistance method of bulk-checking your contact's phone numbers, fine. Just give me the choice of joining without it.
That’s a private gain at the network’s cost. For a challenger, their decision to bar that albeit limited form of free-riding is perfectly rational. For a dominant network, I am much more sympathetic to the call for anonymity.
Why would messengers without phone number collection not be usable by anyone with a smartphone?
Even if that was the case, " it's strictly less usable than WhatsApp" is not true, because other messengers can provide other quality of life features.
" That means in practice, it's unusable." is not true either. Remove "Status" support from WhatsApp and you get strictly less usable than WhatsApp. Still, it is not unusable.
Signal is pretty close to being strictly less usable than WhatsApp btw.
