These two sometimes get confused, but if you want to land your kick, you've got to aim high. I'm assuming (optimistically) that you don't want to waste your time, also that you don't want to add to the sum of gratuitous misery in the world. There are already plenty of people out there stirring the contents of the communal honey bucket without our joining in. For the sake of clarity, here are a few of the forms that shit kicking can take:

Pretending that disagreement is a sure sign of stupidity (on our opponent's part, natch).
Pretending that disagreement is a sure sign of moral depravity (ditto).
Bitching and moaning about things we can't possibly change.
Bitching and moaning about things we could change, theoretically, if we didn't have more pressing things to do.
Taking the view that most or all of our sins are sins of omission, while other people are willfully obnoxious and/or out to get us.
Hairsplitting, nitpicking, all kinds of uninvited grooming.
Temper tantrums.

These are all pretty well guaranteed to take us nowhere fun or even interesting. Ass kicking, in healthy contrast to shit kicking, is ideally a skilled and deliberate action, even a joyful one, designed to promote forward progress.

I want to be clear: I'm talking human butt here, figurative butt. No other animal has a figurative butt to kick - kindly leave their real butts alone.

There's no magic formula to ensure that our efforts are well-spent. Ass kicking is a trial-and-error endeavor, in which only results will tell. But there are a few things we can do to tip the long-term balance in a positive direction:

Name names. Ours and the other guy's/gal's. There are significant exceptions, but by and large anonymity promotes cowardice and impedes learning.
Focus on substance over trivia.
Try to remember that whatever nutty thing the other gal thinks/does/believes, it's working for her somehow. No one is an idiot when it comes to her own immediate interests (though most of us are idiots regarding our long-term interests).
Answer the question: who gets helped here? If "I do" is the only obvious answer, the real answer may be "no one."
Start from common ground. If we can't find it, we need to create it. Here's the weird part: the other party doesn't need to believe it's there, but we do. Failing that . . .
Walk away when the quicksand has only reached our ankles.
Be ready - be hungry - to learn. Embrace the real possibility that our own butts will be smarting when we're done.

Contrary to popular belief, ass kicking takes discipline and trained intelligence. It's a mighty calling, not to be undertaken lightly.

Forza!
Gretchen