Sen. Carl Levin (D-MI) gave a floor speech today in the continuing debate over the "nuclear option." In it, he quoted the late Republican senator from Michigan Arthur Vandenberg from a speech he gave on a proposal by then Vice President Barkley to change the cloture rule to end filibusters:

“...[T]he rules of the Senate as they exist at any given time and as they are clinched by precedents should not be changed substantively by the interpretive action of the Senate’s Presiding Officer, even with the transient sanction of an equally transient Senate majority. The rules can be safely changed only by the direct and conscious action of the Senate itself, acting in the fashion prescribed by the rules. Otherwise, no rule in the Senate is worth the paper it is written on, and this so-called ‘greatest deliberative body in the world’ is at the mercy of every change in parliamentary authority.”

The idea that the Senate's presiding officer can at any time arbitrarily interpret the Senate's rules is exactly what makes the "nuclear option" so nuclear. With the setting of that precedent, what is the point of established Senate rules anymore which lay out the proper procedure for the Senate to make its own rules? The answer is there is none.
More from Sen. Levin:

Mr. President, the “nuclear option”– this extra-legal changing of the Senate Rules– will cause a permanent tear in the Senate fabric because it violates a deeply held American value: playing by the rules. Our rules themselves provide the process for changing the rules. Using an arbitrary way, the Presiding Officer ruling by fiat, will produce a deeply embittered and divided Senate because it tears at the heart of the way we operate as a Senate. The Presiding Officer is supposed to be an impartial umpire, not a dictator. He is supposed to apply the rules, not rewrite them.

Those who are in favor of invoking the "nuclear option" are saying in a most obvious fashion that the end does indeed justify the means.