[justsomehnguy]

Yes, because most people actually want to be reached by people who are yet not in the contacts.

The only way to do so is to have a username or phone number of recipient. Usernames are searchable if they are "Public Usernames". Phone number could be hidden from anyone.

I don't see how someone can contact somebody on the messenger yet without an ability to.. actually send a message. Sure, there could be an option to block everyone not in the contact list and use some other medium to relay the contact request[0] but most of the time this is useless for messenger.

But of course I have my POV skewed, because I prefer to use services defensively from the start so I had almost no unsolicited messages on Telegram, WhatsApp and Instagram.

[0] Hey, if you interested in $TOPIC contact me on Telegram, @username! But first send a couple of avian carriers with your phone number and username so I could add you to contacts first!