Does the US Constitution specifically grant the government the power to interfere in X? If not then doing so is unconstitutional, because the constitution explicitly states (repeatedly, in several different ways) that the federal government has *only* those powers granted to it by the constitution. Which is why something as simple as banning alcohol required a constitutional amendment.
Not exactly. For one thing, whether the US Constitution explicitly grants the Federal government to "interfere in X" is subject to interpretation, and has to be because the US Constitution makes a lot of common sense assumptions about how government works: that's why so many early Supreme Court rulings invoked (British) common law. The critical catch-all clause in the Constitution is Article 1 Section 8: "To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof." Even at the time of the drafting and ratification of the Constitution people debated the degree to which this clause expanded the powers of Congress.
James Madison argued in Federalist 44 that because it would be futile to attempt to anticipate all of the specific powers Congress (and the Federal government) would need for all time, the Constitution *must* grant the federal government any power necessary to fulfill the obligations the Constitution proscribes. He directly stated that trying to enumerate all of the powers the Constitution grants with explicit text would be ridiculous.
Because the question of what is "necessary and proper" is not an absolutely objective standard and the drafters of the Constitution knew this the Constitution can't be said to express explicitly enumerated powers. Even strict constructionists concede at least some of the power granted by the Constitution is implied by the intent of its text and not explicitly stated. And if you're concerned about any expansion of the Constitution's powers as being power-mongering, consider this: the Bill of Rights does not guarantee anyone in the US actually has those rights: it guarantees that the Federal Government can't intrude on them. Nothing anywhere in the text of the Constitution explicitly prohibits state governments from trampling all over, say, someone's First Amendment rights to free speech. The notion that state governments must honor the same limitations that the Constitution places upon the Federal government is another one of those power-mongering BS interpretations of the Constitution, namely the incorporation doctrine of the Fourteenth Amendment. Read the 14th Amendment: nowhere in the text does it say that States must incorporate the protections of the Bill of Rights, and nowhere in the first ten amendments does it state those protections apply to State governments, only the federal government. The incorporation doctrine of the Supreme Court was created over fifty years after the passage of the 14th Amendment, and argued that the implication of the due process clause of the 14th Amendment implies State governments must incorporate the same protections as the Federal government. But try to find that in the text.
Incidentally, the eighteenth amendment which prohibited the sale of alcohol doesn't prove that banning alcohol requires a Constitutional Amendment. The opponents of alcohol pushed for a Constitutional Amendment because it was the strongest possible ban they could strive for and they felt it was achievable. Not only could they ban alcohol sales in every State without having to convince every state to ratify the amendment, once ratified the only way to overturn the ban would be to generate enough support to amend the Constitution again: the ban could not be trivially overturned the way any Congressional law can be by successive Congresses. Its also important to note history: the (anti-alcohol) temperance movement was a very politically powerful special interest back in the day. They wielded significant power over elected officials in state legislatures. The 18th Amendment that banned alcohol sales was ratified by state legislatures, pushed strongly by temperance supporters. But the 21st Amendment that repealed the 18th Amendment was ratified by state ratification conventions which bypassed state legislatures and essentially took the matter to the people directly (via delegations to the state convention). In other words, the reason why Constitutional Amendments were the battleground for prohibition has as much to do with the political landscape of the time as anything else. The temperance people had the stranglehold on state legislatures and could get a Constitutional Amendment passed via state legislature ratification, but when opposition to prohibition reached high levels among the people Congress was able to get a separate Constitutional Amendment passed that revoked prohibition that didn't need their support.