How to win an argument by not arguing.
Consider this a lesson in socratic jujitsu. Business Insider had an article recently on how to win an argument. See: http://www.businessinsider.com/how-to-win-an-argument-2014-5
Their answer. Don’t argue or debate. If you want people to agree with you, instead of telling them why their ideas are stupid, ask them to discuss how their proposed solution would work – step by step – give them the benefit of the doubt.
What this does is changes what is happening from a debate to be won to a problem to be solved. And you have engaged them in the problem solving process. As you ask questions about how exactly their proposal would work, you can help them find out their proposals weak points in a way that isn't threatening. Again, this is you trying to help them make a solution that will work – starting where they are – with their proposal.
As they work through the details, it will be obvious where the weak points are and how to shore them up and to fix them so that the proposal works. All without actually arguing.
So if you want to win an argument, stop arguing. Stop debating. Foster inquiry instead.