That is left up to the states and municipalities.
The states and municipalities should be able to decide whether or not drugs are illegal.
The only thing the feds add is armament, prosecutarial succession beyond the lifetime of the perpetrator and military gear and tactics.
First, there are federal laws for murder, as well as other crimes that cross state boundaries in certain circumstances. We even have a federal force called the FBI to investigate crimes that cross state boundaries. Some of those laws I might argue are outside the federal authority, but not all of them.
And we were talking about legalizing drugs and abandoning the war on drugs, not simply removing federal penalties. But certainly the federal government has the right to control commerce the crosses national boundaries, since it explicitly has the right to regulate interstate commerce AND to deal with other nations.
But really, we were discussing all levels of government, not just federal law, if we were going to legalize drugs.