I think the simple answer is found in the Internet Protocol itself. MAC addresses are only sent within a local area network for routing purposes. The MAC address of an individual computer is stripped at the gateway (however you want to define that), and the MAC address of the gateway is usually used for routing purposes. Thus, the MAC address seen at the IRC server, if one is seen at all will not be the right one. Actually, it is likely to be the MAC address of the IRC network gateway - so choosing that MAC address is likely to kill all traffic.
There - a much simpler explanation without bringing the "might of the US Defence, defender of the entire world" into it!
p.s. Perhaps you want to re-read your history on the origin of the internet? As well as reading up the roles of IP, TCP and UDP. Your ignorance is showing.