i mean facebook gives you the means to provide alternate contact points(phone numbers) to your friends. people don't choose to use it coz of whatever reason deserve to be cut off-why wouldn't you want your friends phone numbers in your phone?
Nowadays the means of keeping contact information when making new friends is whatsapp or facebook. So yes, this would not be a problem for now, but it would be in a few years when mobile numbers become really obsolete (hopefully not).