In keeping with Common Dreams rules of engagement, a reasoned reply is more appropriate than responding in kind to your snark.
You're very strong on making opinionated claims that are unsubstantiated with facts. Most folks simply won't take the time to call you on such obvious falsehoods but since you called me out and I'm taking a minute or so from my garden, I'll take your bait.
You seem to be under the misunderstanding that the Constitution was written in stone rather than created as a living, evolving document. ie: "You believe in a living Constitution, an impossibility for rational people..." Contrary to your "rational" opinion, the Constitution was designed to evolve with the times in a number of ways including through the SCOTUS as well as the amendment process. You may not "give a crap" for the system that the Founder's created but that's the system we live under now and you best get over it rather than resort to revisionist history to justify your neo-Confederate views.
You said, "I could cite a dozen examples right now that were decided by the SC that set REgressives hair on fire that were clearly unConstitutional..." Then why didn't you cite the examples you brag about? BTW you sarcastically criticize others for their lack of grammar and spelling while you misuse the term "REgressive" (sic). At the risk of stating the obvious, regressive is the counterpoint to progressive. When you use the word "regressive" you're in fact referring to conservatives who disdain change. Conservatives prefer looking back "regressive" rather than looking forward "progressive". Your contempt for a Constitution that was designed to be changed puts you in the camp of regressives. In that regard, you should be proud of being a regressive.
Moreover, it's worth noting that much of your opinions rest on the type of government we had pre Civil War. The Civil War changed everything and Lincoln consciously outlined those changes in his Gettysburg address as well as through the 13th, 14th, and 15th amendments. Just one small example is the fact that before the CW the term "United States" was plural as in "The U.S. are working toward building economic ties with Europe." After the CW the term "United States" was singular as in, "The U.S. is working toward...." We became a true nation after the CW instead of a loose confederation of states which was what the Confederate states wanted. By keeping the Union together, Lincoln of necessity required and created a strong central government. You may not like that fact but no amount of revisionist history on your part will change it.
BTW it's worth noting that during that same time period, Lincoln began the building of the trans-continental RR just as Repub Eisenhower began the building of our transcontinental hwy system. Both were projects designed to unify and bind us economically and culturally as a nation under a federal government. In other words, you're living in the pre Civil War past and your defunct libertarian, neo Confederate arguments reflect such.
You said, "...the US spends almost 4% of it's budget on infrastructure vs 3.1% in Europe..." This is an example of your deceptive use of statistics to obfuscate. The truth is that you cherry picked your statistic from the results of Obama's American Recovery and Reinvestment Act of 2009 which temporarily expanded funding for infrastructure. In other words, the very gov. spending you disdain, you then conveniently try and use to prove a point.
The truth is that for the past 20 yrs, with the exception of Obama's stimulus plan, the U.S. has spent only 3% of GDP on infrastructure. Prior to that it was 6%. Meanwhile you conveniently overlook the fact that your much touted "smart money" military spends 22% of our GDP on such debacles as the F-22 and F-35. The military is the exemplar of the "crony capitalism" you disingenuously decry.
Then there's this piece of falsehood, "What is bankrupting the PO is an insane defined benefit pension plan as this same thing has bankrupted innumerable cities and states across the country." "How is the GOP "trying" to bankrupt the PO?"
To answer your question:
Latter day, neo-Confederate, Repubs in Congress hate the gov. mandated USPS because they hate our government by their own admission. They've tried to destroy the USPS with a thousand cuts by privatizing many of its functions as well as unique mandates on its pension system which you mischaracterized. In that vein, Congressional Repubs pushed legislation requiring the Postal Service to prefund retiree health benefits for 75 years into the future in an effort to bankrupt the USPS. The cost is staggering: as much as $5.8 billion per year to pay the benefits of future postal workers who aren’t even born yet. No "defined benefit pension" anywhere suffers under this "insane" mandate. However, based on your pre Civil War argument, one would have to assume that you're in full support of the USPS since it was enshrined in the Constitution by the Founders and is thus constitutionally protected pre Civil War, which is why Repubs have not been able to do away with it entirely.
I've already spent too much time here but it's worth it for the benefit of others who can't spend time addressing all of your obfuscation, falsehoods, revisionist history, pie-in-the-sky libertarian arguments and snark. It's become necessary for those of us on the other side to begin to confront the Fox/Murdoch talking points; the neo-confederate revisionists; the Pat Robertson fundamentalist theocrats, and more...if we are to ever bring our nation back from 30+ years of sliding backwards.
It's not just regressive, conservative scorn of Amtrak as stated in the article's title that's the problem. The root of the problem is conservative scorn of our government and thus our nation. The two are inseparable. Your obvious scorn for our government is a case in point.