Discussing security for the three countries and the ways we can cooperate to do that is a good thing to discuss. What this taskforce is suggesting is something else, a relaxation of national borders between the countries. Quite different.
It should be noted that Lugar has introduced a bill to include Central America in the perimeter security.
Another of the main reasons behind this is to allow US interdiction forces to operate in Mexico. This has always been the key for intervention of terrorists, drugs, and illegals. Mexico has resisted this because of sovereignty reasons but said that they would go along if the US would reform immigration policies.