As set forth in the preamble, the purpose and intent of the Constitution is to (among other things), "...provide for the common defence, promote the general welfare and secure the blessings of liberty to ourselves and our posterity." If they intended the document to be in effect for people born 200 years after its adoption, surely they meant for it to apply to those born within nine months of its adoption. Anything that would deprive persons (born or unborn) of the Constitution's applicability would be at best, inconsistent with, and at worst, in direct opposition to, the stated purposes of the Constitution, ergo, "unconstitutional".
IMHO, one must delve into the "penumbras and emanations," to argue otherwise.
http://www.foundersrevolution.net/2011/10/on-general-welfare.html
I might agree with you that you don't have to read past the Preamble if I had never read past the Preamble, or devoted any time to researching the Constitution, or read history beyond the New Deal. I've spent no small amount of time researching the Constitution, the different methods of interpretation, and the history of it's creation and the debates and discussion that produced it. All of that tells me you are very much mistaken about what power that sentence was intended take from the states and give to the national government.