The purpose and meaning of the general welfare power was open for debate from the very first. Even Madison and Hamilton, who both wrote some of The Federalist Papers, did not agree on what it meant.
Correct, Madison and Hamilton did not agree on its meaning. But their separate opinions on the matter, were very close, especially when compared to some of the loony "interpretations" floating around today.
James Madison held that the General Welfare clause had absolutely no impact whatsoever. It did not grant Congress any additional authority for anything, he said - Congress was authorized to exercise ONLY the powers EXPLICITLY spelled out in the Constitution and its amendments.
Alexander Hamilton believed that the General Welfare clause did authorize Congress to exercise additional powers that were not explicitly spelled out in the rest of the document. But even Hamilton maintained that these additional powers were extremely limited: Only powers that benefitted all Americans equally, were authorized to the Federal govt by the GW clause. Powers that might benefit only selected groups, or individuals (what we now call "special interests"), were still forbidden to the Fed in Hamilton's view. Madison, of course, agreed with this last.
In a Supreme Court case in the 1930s (I believe it was US v. Butler), the Supremes ruled that Hamilton's view was the correct one. The GW clause authorizes the Fed to engage in programs that equally benefitted all Americans, even if they weren't spelled out in the Constitution... but the Fed was forbidden to involve itself in programs that benefited only partial groups or individuals.
Contrast that to the loony left's view that the GW clause authorized the Fed govt to do anything it pleased, anywhere and to any extent, as long as somebody benefitted someplace. If that were true, the Framers wasted their time writing most of the rest of the Constitution, because the powers it specifically authorizes could ALL be granted to the Fed under such a huge "Welfare clause". Obviously, this was not the Framers' intent, and the Supremes agreed it was not, in that 1930s case.
the Constitution was written to be interpreted so it can be adapted without risking amendment that could completely destroy the document.
That's one of the weirdest and most self-contradictory statements I've heard about "interpretations" of the Constitution, and I've heard a lot of them.
Only a very few parts of the Constitution are left open to "interpretation". They are well known: What are "unreasonable" searches and seizures; what is "probable cause", etc. These interpretations are left to judges to decide on a case by case basis.
The idea that it can be adapted by further "interpretation", goes flatly against both the letter and spirit of the document. As the Supremes have pointed out many times, the idea of such flexible adaption, would obviate the very purpose of having a written Constitution in the first place. It would create chaos (as we are seeing increasingly today) as one official interpreted it one way today, then another interprets it differently tomorrow, etc.
Even if just one group (such as the Supreme Court) were in sole charge of all such "interpretations", the chaos would continue as they "interpret" one way today, let the country align its activities to that "interpretation", and then "interpret" it a different way in a month, or a year, or in a decade. The very principle of "stare decisis" comes from the grim agreement that changing a previous decision carries grievous costs, and should be avoided unless absolutely necessary. (This sentiment was noteably absent after FDR's attempt at packing the Court, when it started overruling its previous decisions wholesale and implementing policies that violated the Constitution it was sworn to uphold. The senitment returned, though, once the new socialistic policies were in place, and the leftists rediscovered a desire to see them remain as they now were.)
The backbone of the Constitution, is the idea that the powers of the Federal govt are limited to those granted by the Constitution (including the slightly expanded powers supported by Alexander Hamilton), and that it may have NO OTHER POWERS unless the Constitution is formally amended by procedures laid out in Article 5 of that document.
Permitting the bizarrely flexible power to change the Constitution by "interpretation" as you have described, would not reduce the risk of "amendment that could completely destroy the document" as you claim. Formal amendments could still be proposed and ratified. But the flexible "interpretation" you seem to want, would merely add another avenue to destroying the document, even more easily. If there were no other reasons to shun such bizarre "flexibility", that would be a good one. But there are plenty of other reasons to reject it, too.
The Constitution's adaptability gives it stability
If that were true, it would be the purest nonsense. Fortunately, that bizarrely extreme "adaptability" doesn't exist, except in the minds of a few government-uber-alles fanatics who hate the restrictions the Constitution places on Federal power.
As I have pointed out, such extreme "adaptability" would directly destroy the very "stability" you claim to want, and lead only to chaos.