"Is it OK to use foul language in a political discussion?"
I'll steal a great line from Talleyrand here and say, "It's worse than a crime ... it's a blunder."
In a political discussion, you should have at least two aims:
(1) To learn what your opponent believes, and why. Know your enemy. And you want his best arguments. Especially since occasionally, he may be right. Foul language on your part inhibits this process.
(2) To refute your opponent's arguments, with better ones, so that
(a) You influence 'neutrals', and pull them towards your position, ... and foul language is not likely to impress them.
(b) You plant the 'gnawing worm of doubt' in your opponent's mind -- insulting them personally gets in the way of doing this.
(c) You reinforce the beliefs of people on your side, both by showing them that there are good arguments for your shared beliefs, held by people who are not-stupids, and by giving them these arguments to use themselves. Again, foul language, and indeed any language of the sort 'you are evil/stupid/etc' gets in the way of this.
I've seen many threads in political discussion forums where one side -- usually, I'm sorry to say, the Left -- makes a powerful argument, or at least one which on its face is powerful -- such as presenting a graph showing that 'Red' states have more violent crime than 'Blue' ones -- and which the people on the other side cannot immediately answer ... and this provokes from them just a flurry of insults. Nothing says "We lost the argument!" than a lot of nasty personal insults.
But let's not be too goody-goody here. The occasional foul word can be very powerful, if it's carefully chosen. These words exist in our language for a reason. For example, as a sudden shocking contrast, as in the following joke:
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A young novitiate arrives at a to begin her training as a nun. After she has been in the convent just a few days, the local golf course offers free golfing lessons to all the nuns, and she signs up for them and goes with other nuns for her first lesson.
But in just a few hours, she returns to the convent in floods of tears, very upset. She is ushered in to see the Mother Superior, who sits her down and asks, "What is the matter, dear?"
"Oh, Mother, Mother", cries the young nun, "I blasphemed!!! I insulted the sacred ears of our Lord by taking His name in vain and saying terrible things!!!"
"Now, now, dear," the Mother Superior says soothingly. Our God is a loving God and a forgiving God. We all make mistakes. What was the occasion for your blasphemy?"
"Well," the young nun answers, "after our lesson, we all went out to the green to play a game. And my very first shot was almost perfect! It went at least half way to the first hole ... but then, as it hit the ground and rolled to a stop ... a squirrel ran out and grabbed the ball and begin to run off with it!!!"
"There, there, dear, " the Mother Superior replied, "why, anyone would have blasphemed at something like that... "
"No, no," cried the young nun. "I remained composed and said nothing ... but then ... as the squirrel was running away with the ball, an eagle dropped down out of the sky, and grabbed the squirrel in his claws, and begin to fly away with the squirrel and the ball!!"
"My goodness!" exclaimed the Mother Superior, "Why, anyone at that point would have blasphemed!!"
"No, no, Mother," sobbed the young nun ... "Even then, I did not utter words of blasphemy ... but .. as the eagle flew over the pond that is near the first hole, the squirrel dropped the ball, straight into the pond!"
"Extraordinary!" exclaimed the Mother Superior, "Satan at work! Well, I sure God will forgive your blasphemy at that point and..."
"No, no, no," interrupted the young nun. "Even then, I said nothing. And the ball fell straight down, and hit a turtle's hard shell, and bounced out of the pond, and .... it rolled to within a few feet of the first hole!"
"Stop!!!! Now I understand," said the Mother Superior, holding up her hand. "Now I know what happened... you need say no more ...and I am quite sure God will forgive your blasphemy ... I know exactly now what was the occasion of your blasphemy, something that would have tried the patience even of God Himself. You were provoked beyond human endurance, because ...
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... You... Missed... The... Fucking... Putt!"