A stamp can cost as little as 0.1 sat, or even 0.01 sat.

It's not retarded if you're a young individual thinking of ideas. But it doesn't work because there aren't enough sats to go around. Bitcoin doesn't subdivide small enough. There are already people on earth who can't afford to spend 1 sat to send any number of messages on the internet. Possibly a mistake by Satoshi, possibly just him not wanting it to be used this way, not sure

using Bitcoin is the only solution that works without a central authority