Argue, but only in the name of progress, not in the name of victory. Attacking or judging someone will not help you influence them. Communicate to the other person inarguable facts to get to your true point.
Share your sensations: what did this made you feel and where in your body; be precise.
Share your emotions: how did this really made you feel, sad? Mad? Angry? Maybe even glad or relieved about something? Again, be specific.
And lastly, share your "why": what do you want from them (or maybe even from yourself), what's your endpoint? What would you like to see changed and what do you think this change would accomplish?