Also, while your anecdote may be interesting (to you), you're still evading the issue. Clearly in this country there are instances where a person could be murdered and this crime not be covered by state law. According to you, this crime could not be prosecuted, because any federal law against murder is unconstitutional, yes?
The only case that I'm aware of is if the crime takes place on a Federal installation or territory over which no state has jurisdiction. In that case, I have no problem with a federal law and federal prosectution. On the other hand, I believe in the 10th Amendment: "The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people." Stretching the 5th to defend Federal laws about abortion seem to me to be changing the meaning of the Constitution. We'll see when the South Dakota case comes to the SCOTUS.