I should recognize that's the most understood definition today.
Here's where I'm coming from in my own uneducated usage:
The Man with the Muck Rake
By Theodore Roosevelt
April 15th, 1906
{snip}
In “Pilgrim's Progress” the Man with the Muck Rake is set forth as the example of him whose vision is fixed on carnal instead of spiritual things. Yet he also typifies the man who in this life consistently refuses to see aught that is lofty, and fixes his eyes with solemn intentness only on that which is vile and debasing.
Now, it is very necessary that we should not flinch from seeing what is vile and debasing. There is filth on the floor, and it must be scraped up with the muck rake; and there are times and places where this service is the most needed of all the services that can be performed. But the man who never does anything else, who never thinks or speaks or writes, save of his feats with the muck rake, speedily becomes, not a help but one of the most potent forces for evil.
There are in the body politic, economic and social, many and grave evils, and there is urgent necessity for the sternest war upon them. There should be relentless exposure of and attack upon every evil man, whether politician or business man, every evil practice, whether in politics, business, or social life. I hail as a benefactor every writer or speaker, every man who, on the platform or in a book, magazine, or newspaper, with merciless severity makes such attack, provided always that he in his turn remembers that the attack is of use only if it is absolutely truthful.
The liar is no whit better than the thief, and if his mendacity takes the form of slander he may be worse than most thieves. It puts a premium upon knavery untruthfully to attack an honest man, or even with hysterical exaggeration to assail a bad man with untruth.
An epidemic of indiscriminate assault upon character does no good, but very great harm. The soul of every scoundrel is gladdened whenever an honest man is assailed, or even when a scoundrel is untruthfully assailed.
Now, it is easy to twist out of shape what I have just said, easy to affect to misunderstand it, and if it is slurred over in repetition not difficult really to misunderstand it. Some persons are sincerely incapable of understanding that to denounce mud slinging does not mean the endorsement of whitewashing; and both the interested individuals who need whitewashing and those others who practice mud slinging like to encourage such confusion of ideas.
One of the chief counts against those who make indiscriminate assault upon men in business or men in public life is that they invite a reaction which is sure to tell powerfully in favor of the unscrupulous scoundrel who really ought to be attacked, who ought to be exposed, who ought, if possible, to be put in the penitentiary. If Aristides is praised overmuch as just, people get tired of hearing it; and overcensure of the unjust finally and from similar reasons results in their favor.
Any excess is almost sure to invite a reaction; and, unfortunately, the reactions instead of taking the form of punishment of those guilty of the excess, is apt to take the form either of punishment of the unoffending or of giving immunity, and even strength, to offenders. The effort to make financial or political profit out of the destruction of character can only result in public calamity. Gross and reckless assaults on character, whether on the stump or in newspaper, magazine, or book, create a morbid and vicious public sentiment, and at the same time act as a profound deterrent to able men of normal sensitiveness and tend to prevent them from entering the public service at any price . . .
speech:
http://www.quotedb.com/speeches/man-with-the-muck-rake