There are a couple of reasons why you are so good at arguing and have a sharp tongue.
First I feel most strongly that your Libra Mercury square Uranus gives you the ability to say things abruptly before you have had the good sense to think before you speak. Uranus hates anything boring so there is a natural tendency for us to allow our Uranus Energy get us into hot water, so to speak.
Mercury is how we communicate. How we think. How we speak. A square aspect is when two planets are closely within 90 degrees. A square is a personal discontent that we need to work on. I call them Life Lessons. So with this hard aspect between Mercury (communication) and Uranus (abrupt change), I imagine you have a really bold and impulsive way of speaking when you are not happy about something. I imagine the words are off your tongue before they have even made it through your brain circuitry.
Mercury square Uranus is a trip. You probably have shocked a few people (or more) throughout your life due to this square that can really get others panties in a bunch. Particularly traditional conservative elderly people. Or people that aren't elderly. You have the potential to shock others when you open your mouth. That is the bottom line. This is a life lesson for you.
Sure would like to see some pictures of the people's expressions when you belt out something shocking with your sharp tongue. A sharp tongue is a perfect way to describe Mercury square Uranus. You might want to work on this because you want to make as little new negative karma as possible so you don't have to "Pay Up Later." Karma does balance all.
And I think the reason you are so excellent at arguing is due to your Libra Sun. Libra's Symbol is The Scales of Justice. So Libras just have a way with debating with others and actually winning too! They are great mediators, probably the best of all the signs of the zodiac. So your Libra Energy is why you are so good at arguing, or to put it more kindly, debating. You just have a gift from a previous lifetime in which you developed this ability to see both sides of an issue. That is what Libra does so well. They also "balance" as they ARE the Scales. Just like karma. Much balancing going on here.
And that close conjunction of Mercury at 17 degrees Libra and Venus at 16 degrees Libra also gives you the gift of being a kind communicator when you so desire. I'll bet you can be sweet as honey when you desire something or need a hand with something too. Venus so close to your Mercury shows that you can be a wonderful speaker also. Mercury=Communication and Venus=Love. This is an aspect of one that CAN have a beautiful voice, at least when you aren't allowing Uranus to join in anyway.
So all that Libra gives you a great ability to debate (or argue, however you want to put it). And that hard Mercury square Uranus gives you the courage to say whatever you WANT to say. You are not shy about voicing your opinion. We need people like you. However you might need to "tone it down a few notches" at times and then let that SWEET Venus conjunct Mercury working in order to get your way.
Hope this is helpful and good luck and bless you too. I wish you well. Very respectfully as I do not want to be on the receiving end of the Mercury/Uranus square. lol