Wrestle With A Pig Meaning

(idiomatic) To engage in a struggle with an opponent that benefits from the struggle even without winning it.

Example: 1946, Richard Percival Calhoun. "Moving ahead on your job", McGraw-Hill.
  "And when you begin refuting one another's reasons, fussing back and forth, you generally do what a nationally known industrial relations authority warns you against: you wallow in the mud with the pig. He says, 'Never wallow in the mud with a pig, because the pig likes it.' That is exactly what he wants, because you are on his home ground. He can think of arguments as well as you can, so where do you come out?"
1950, Time, volume 56.
  "'I learned long ago never to wrestle with a pig,' Ching likes to say, 'You get dirty and besides the pig likes it.'"
1957, Barney Glazer's Column, The Loris Sentinel, Feb 13, p4.
  "Whenever a boisterous and argumentative person cries to draw you into a public discussion or a wrangle, just remember this bit of advice. "Don't wrestle with a pig. You'll get dirty which is exactly what the pig likes."
2002, Dinesh D'Souza, Letters to a Young Conservative, p 23
  "While I was at the Dartmouth Review, we used to tell the deans that taking on our campus paper was like wrestling with a pig. Not only did it get everyone dirty, but the pig liked it!"