If you have ever played the board game "Risk", you will realize it is a heck of a lot easier to defend North America than the US by itself. No way in except through Panama or by boat!
We've done fine for a couple of centuries. The oceans have always helped.
The only reason Mexico is a vulnerability is because...it's Mexico, they hate us, and they want our country. Mexico is the problem, not the answer.
PS: it's truly nauseating to hear that Doris Meissner is still walking around free. If everyone recalls, she was the one who decided that illegal aliens had more rights than Americans, and basically dropped all immigration enforcement in the 1990's, leading to 9/11.
Yes that is true conventionally speaking, though I don't see many conventional wars in the future. If there is I also don't see the Mexican megaforce coming to our rescue or the Canadians building up enough military to matter. I see US being stretched even thinner. Now your point is well taken, about a potential land attack thru Mexico and is something to consider but at this time with the second amendment still in tact (this will amended out of the constitution within a decade of these agreements being implemneted) I think we certainly could lend a hand to our military if such a thing occurred. But its not just about a Military perimeter, its about an economic one first and foremost.
Also, whether in real life or a board game, one thing remains constant, smaller boarders are easier to protect.
Lastly, if we view the entire North American continent is viewed as one entire area to protect, who do we trust to protect it? Do you propose that we integrate our military with a Keystone Cop military of Mexico? What about Canada? There government regularly displays contempt for us and our ideals, would you have us integrate with them?
One more lastly, who really benefits from this? Granted our industry gets cheap labor, but in the long run, the burden is put upon the entire US tax payers, as it is OUR military that will be proping up Canada and Mexico. It will be OUR economy that will drive the economies of Canada and Mexico. It will be OUR taxpayers that will pay the taxes for all the social programs in Canada and Mexico.
24 kt gold is considered the purest MOST VALUABLE gold. Lesser kt wght is contaminated with other impurities, therefore LESS VALUABLE. Mixing in Canada and Mexico with the United States, is nothing more than diluting our strength, our economy, our values, and our overall worth. In essence, it dilutes everything that makes the United States THE GREATEST NATION ON EARTH.