Why MAC filtering is poor wireless security

MAC filtering on a wireless access point is easily bypassed. Many organizations use MAC filtering as a means of keeping non-paying customers off of their wireless network. I have seen 2 basic implementations of this :
1. Device can't read or pass any traffic across the network unless its MAC is in the list.
2. Device can read but can't pass traffic(except ARP/DHCP) across the network unless its MAC is in the list.

Both 1 and 2 can be bypassed by using Kismet and listing the connected devices. The attacker then spoofs his MAC to look like an authenticated device. 2 can also be bypassed by connecting to the access point and using Wireshark to see which devices are sending TCP traffic. Once again the attacker spoofs his MAC address to look like a device that is sending TCP traffic.