Any document with a political process for amendments isn't really a protection at all. Ask any former slave owner about their constitutionally protected property and the lack of compensation (except you can't because they are dead).
If in 2240 America's demographics are dominated by Islam and they elect a majority in the house, senate and control the presidency, do you think a piece of paper is going to stop a constitutional amendment imposing sharia law?
The Treaty of Troyes did nothing to stop Valois from taking the throne of France from Plantagenet. That was a flimsy paper shield too.
As for the letter, I'm perhaps not as familiar with US politics as I should be, but to me I don't see how that person finds the republicans unappealing?
Is that points 3 and 9 through 12?
I think America would improve greatly if they had a Constitutional amendment protecting its citizens from pork spending.