[Seems like an idea that wasn't subjected to much scrutiny before it was implemented.
Like many ideas from the early days of the internet, it was part of a panic response by the ISPs to the very real threat of severe economic penalties even revocation of operating licenses by state and federal regulators responding to the totally unexpected tsunami of SPAM flowing through the ISPs networks and threatening to overwhelm the nascent internet industry. Even though there may be better techniques available today, the old ones are seldom, if ever, revisited because regulators, developers, users, and investors are too busy damming up the new waves of SPAM that come up daily even hourly.
