One of the less known and more controversial moments in the history of the Constitution of the United States was the 17th amendment of 1913. It birthed what some claimed was a more fair and accountable political system, and what others called Unconstitutional, tyrannical, and the removal of the voice of the States at the seat of government.

http://livingnotsurviving.com/2013/06/18/the-argument-to-repeal-the-seventeenth-amendment-of-the-constitution/

Heck,that's how we have been electing our Upper Chamber(Senate) ever since,by Popular vote by the States!
A measure to elect the Federal Council(Cabinet) by popular Vote was just rejected by the People in a Vote a couple of Weeks ago by about 3 to 1!

Uh, calling an amendment to the U.S. Constitution "unconstitutional" is non sequitur.

In a way it is and in a way it is not. Congress constantly passes bills that violate the Constitution. An amendment to the Constitution that violates the original intent or negates other sections can be said to be "unconstitutional" and it is up to someone to reject it, and bring it before the Supreme Court for a determination.

Uh, a bill passed by Congress isn't the same thing as a constitutional amendment. Constitutional amendments require ratification by 2/3 of the states.

that's about how we do it here,with the exception that the People vote on it instead of the State-Legislature!
But it still has to be approved by the Majority of the Citizens in the Majority of the States!


Constitutional Referendums[edit]

Modifications to the constitution are subject to obligatory vote and require a double majority both of the votes and of the states. Such votes are called when the parliament proposes a constitutional modification, or when 100,000 citizens sign a "popular initiative" that clearly states a proposed constitutional change.

The double majority is not only required of the citizens, but of the cantons as well: Each full canton has one vote, but so-called half-cantons (because they were so historically split centuries ago) only have a half vote each. The cantonal vote is determined by a popular vote among the people of that canton; if the majority supports a proposal then the entire canton supports the proposal.

This cantonal vote means that small cantons are represented equally with the larger ones. For example, Basel-Country as a canton has about 256,000 inhabitants, but has only half a cantonal vote (the other "half canton" being Basel-City). On the other hand, the canton of Uri has a full cantonal vote, but only 35,000 inhabitants.

More than 550 referendums have occurred since the constitution of 1848 (legislative or constitutional).

WIKI

http://en.wikipedia.org/wiki/Voting_in_Switzerland

Uh, I believe that this thread is about an amendment of the U.S. Constitution. So, why mention Switzerland?