It isn't an assumed need. I grew up in the era when schools started to implement this policy in the States. You would get one kid who got no Valentines cards, and everyone would comment on it--"look at the loser". So schools started an "everyone or no one" rule. Same thing with birthday parties--if you hand invitations out at school you have to invite the whole class, so kids don't get the double humiliation of not only being uninvited but being shown up in front of the whole class.

You might view it as "protecting kids from the realities of life"; I don't. I WAS the unpopular kid. I already knew it, I just didn't need or want it flaunted and have everyone effectively pointing and saying "HA HA!" It's softening the edges of child cruelty.

Ghoti, unfortunately I don't know why it's become a schoolchildren's thing--all I know is that it was well established when I was at school. We'd give out little cards and candy hearts.