Just a tip: If you can't argue without name calling or insulting someone's intelligence, please don't argue with your friends"
This really falls cleanly into the "if you can't play nice, please don't play"
I know this is a harder line to tread, and sometimes, in the heated environment of an debate, people can forget themselves and let things slip.
But please, people, please do try. I have noted, over the years, and especially on sites like facebook that this is a particularly hard tip to follow for people.
Understand, I am not suggesting you keep your valuable opinion or dissenting information to yourself. I am not even suggesting you sugarcoat your words.
But there is a not even sort of fine line between stating your opinion in a direct, respectful and well informed manner, and immediately defaulting to insults or demaning insinuations.
But then sometimes I wonder: DO people know they are insulting you when they imply your opinion is stupid without telling you why? Do they know that implying you only think something because you are this color, or from this part of town, or wear converse, is actually really condescending? Do they know that implying any one group is, across the board, stupid and ill informed is just plain stupid and counterproductive, in and of itself? Do they know that jumping down someone's throat without asking polite, clear and real questions just implies they walked in assuming the opinion proffered must be based on a deep deficiency.
I don't know, but they should.
Look, if you respect someone enough to engage in meaningful debate over anything from a pair of shoes to war in the middle east, you should also enter into the conversation with the expectation that they MIGHT know what they are talking about, and that they are capable of understanding what you are talking about. You should assume they are educated to a level in which they can understand the debate you are presenting. If you find they are NOT getting it, letting them know they are stupid or evil or deficient in some manner does not make your point, unless your point is that you are an ass. Educating them, nicely, does a much better job of informing them, and possibly even swaying their opinion. And finally, if you find they are so lacking that they can't even begin to understand your point, back out nicely, because otherwise they probably just come to dismiss you and your opinion even more completely.
Anything else just shows you are looking for a fight. And friends don't go looking for a fight with their friends if they want to stay friends for very long.