"Never wrestle with a pig. You both get dirty, … and the pig likes it."
I once had an Officer in Charge in the Navy who kept that saying on her desk. I have since found out that the first part of it is also the title of a book on business management.
The basic thought is that arguing with a person who doesn't know what they are talking about just brings you down to their level. I have certainly spent useless hours wrestling with religious pigs. One night I wasted two hours arguing with a man about whether the King James Version of the Bible was directly inspired by God. Since he would not accept the idea that the Bible preceded 1611 in both Hebrew and Greek, even though the preface to his Bible said so (but the preface was not inspired), it was useless to continue. It had been useless to begin, but I had yet to learn not to wrestle with pigs. This is not to say that everyone who believes the King James Version is the only inspired Bible, or any other doctrine with which I disagree, is a religious pig. Sometimes you get into a wrestling match thinking the other person is a thinking person, then find out he is a pig.
Paul warned against such wrestling with pigs. "Neither give heed to fables and endless genealogies, which minister questions, rather than godly edifying which is in faith." (1 Tim 1:4) "If any man teach otherwise, and consent not to wholesome words, even the words of our Lord Jesus Christ, and to the doctrine which is according to godliness; He is proud, knowing nothing, but doting about questions and strifes of words, whereof cometh envy, strife, railings, evil surmisings, Perverse disputings of men of corrupt minds, and destitute of the truth, supposing that gain is godliness: from such withdraw thyself." (1 Tim 6:3-5) Such arguments serve no valuable purpose. Jesus, himself, put it a little differently. "Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet, and turn again and rend you." (Matt 7:6)
There is another sense in which we sometimes wrestle with pigs. This way fits the original quote a little better, even than does the idea of arguing with people who don't know what they are talking about. Paul phrased it differently, but with the same intent. "Be not deceived. Evil companionships corrupt good morals." (1 Cor 15:33)
When one wrestles with a pig in this sense, one gets dirty. You never wrestle with a pig and the pig gets cleaner. You may wrestle with a pig and neither gets dirtier, but the odds are against it. So the principle remains. If you choose to associate with those who would lead you to sin, chances are you will end up on their level…and they like it.
Someone called the second chapter of Proverbs Solomon's advice against joining a gang. It certainly would apply to modern gangs, but the application is broader. Solomon is simply giving the same advice as Paul did above. When you wrestle with pigs, chances are you will get as dirty as they.
Jesus died to make us clean. Don't return to the mire. Stay away from the pigs.