argument, meanings thereof:
"a reason or series of reasons offered or available as proof or inducement (with for or against); exchange of such reasons; debate; matter of debate or contention; an unfriendly discussion; a summary of subject-matter; hence contents (Shakespeare); proof, evidence (archaic); a variable upon which another depends, or a quantity or element to which a function, operation, etc applies ( maths, comput., logic ); the angle between a vector and its axis of reference ( maths )"
There you are, soon. As you will see "unfriendly discussion" is only one of many meanings of the word argument. Most of its meanings have nothing to do with unfriendliness, so those of us using its manifold other meanings are correct.