Discovery and preventing spam should not take precedence over privacy for an app that supposedly has privacy as its number one priority.

Privacy isn't signal's one priority.

Good enough privacy for the masses is.

They are always making these tradeoffs, and always make the same decisions. Perfect privacy in every situation isn't the goal. The goal is better privacy than the average person currently has, while still maintaining a level of convenience that the average user well accept.

That's what google and Facebook say.

Indeed. So one must conclude that privacy isn't the top priority.

Why is it is easier to find someone when you can only use one identifier to find them, instead of several? Note that WeChat also uses phone numbers to limit spam, so you can find anyone if you know their number. (But exchanging QR codes is the preferred method of sharing contact information, to the point where I couldn't call most of my contacts except through WeChat.)

> To prevent spam

I suspected that, but have they openly said it? I suspect it's also to deter criminal activity.