Most people just slip it into a sleeve for travel or a laptop bag (which is what i use) in day to day use you should be fine but a computer is a tool and a laptop is one that may find itself in less than safe environments. The chances are eventually it will get scratched thats pretty much the way things are wether its due to the case/ cover /skin you are using or something on a surface you are using it on or the many myriad ways that you can damage it, it will happen, and thats fine thats what happens with tools they get used and it shows.
If your aim is to protect the computer from damage that will stop it working from falls etc then this is a different matter, put the tech 21 armour case back on accept the stains it causes as the inconsequential thing they are and keep using the computer as before, or buy a new case and accept that the reason most people don't use cases is that they are usually more trouble than they are worth for stopping minor surface damage and stains but they may help stop a screen shattering or a corner denting in a fall.