Handshakes far predate modern germ theory of disease. The "danger" doesn't really help with intimacy in any way. It's completely unnecessary danger. We'd find sharing tissues with strangers to be disgusting if it were introduced as a greeting today, but touching the hands of someone right after they've sneezed and coughed into them--after which we often unknowingly touch our own face--is regarded as a sign of intimacy or respect.