Dunbar was playing on a bad knee because they felt we needed him. Our depth at outside corner is just not good right now, and football is a game about depth. You can't be good everywhere and when you get injuries at a spot you were already weak at then things can get out of hand quick. Remember that Thorpe is on IR, JR Reed was questionable, and Amadi and Griffin were both out. The next man up was probably Jayson Stanley who I certainly don't know much about.
Obviously, with the benefit of hindsight knowing that we were going to get stomped we should have just played a young guy for experience and let Dunbar take the week off. Every game in the NFL matters though, and if the offense has a great game today then maybe one more play from Dunbar than we'd get from a practice squad guy could have made the difference.