I think you have the right idea in that you are describing a particular event in your life and using that event to illustrate who you are and why you want to/ think that you can practice law. Because the event has to do with debate and discourse, I think it's an added plus. However, I think you should be very careful in how you approach the prose style of this piece. The above poster said that you should focus on better imagery and whatnot. I disagree. Do not attempt to be novelistic or orotund when writing your PS. Adcoms want specifics, logical reasoning, coherence, and good clear writing. Worry less about how descriptive you are and more about succintness, and, in the process, you will be more descriptive, or, rather, you will describe better. Well, good luck to you. SMU is also one of my reach schools, and I'm feeling the PS pain.