About a year and a half ago I had the same debate question. I opposed the Schengen area and I lost the debate. The previous debate was before the recent waves of Terror in Europe specifically in Germany, France, and Belgium. Also before the Migrant Crisis which has divided European Politics in half with the Citizens of Europe severely upset and fearing what could happen next. I will not be upset if I lose me argument It is only for me to understand other people's perspectives. I have never lived my life in Europe just for your information.
I believe that the Schengen Area is a bad idea. 26 countries, all European. My base reason for opposing is the open borders. There are no border walls. Almost every country in Europe has open borders. The recent terror attacks should demonstrate why this was a bad idea. Think about it. Any terrorist can roam through all of Europe and not get checked even once for guns, passports and other items. Open borders just mean open attacks. While the Schengen area covers about four million square miles, that means bad luck. In conclusion for my first argument, the area is bad because a large portion of Europe's land is considered the Schengen Area.