If God loves us, why did he send the devil back to our Earth after he tried to overthrow our Lord?

The Devil practically owns this entire world, most people sin on a daily basis by his mischievous illusions. For example, commercials... they manipulate your mind into wanting to buy the next 'cool' cell phone. Only a small fraction of people have realized this and thats what makes me so mad... I believe in God completely and i just can't see why he left god forsaken lucifer with us? This is like killing billions of souls. Couldn't he just have destroyed the devil or locked tha mutha a upp?? i mean seriously why do we get him? he's making an army called the illuminati, and i ume he will try to over throw heaven as well as earth and start the new world order (anti christ era). Why couldn't god juust turn him into dust and neva again have to deal with him?