This is seen as a perfect kill system because:
Young Joe is a Looper. He’s had a messed up past, no real parents, and had his lessons on life given to him by a man from the future who gave him a gun and taught him to kill. Needless to say, Joe has issues. He drops designer drugs in his eyes all day, frequents prostitutes, etc. But Young Joe also has heart, studies French, dreams of traveling to “better, more sophisticated” places than Kansas, and gets all vulnerable about childhood and parenting with his prostitute lady friend (Piper Perabo)… Somewhere in that stoic hitman there’s a heart – though often it gets buried beneath the selfish ambition to “get his” in life, no matter what the cost.
When Old Joe (Bruce Willis) arrives, Young Joe is confronted by a possible version of himself that understands the world much differently; Old Joe (as seen in montage) has been down the path Young Joe is fighting so fiercely to go down – Old Joe knows how empty it ultimately is, until you find love. Real love. Old Joe had it for a brief stint of time until his past came back to haunt him (Loopers’ deaths are predetermined, remember?) and cost him the love of his life, as well. Old Joe is fighting for love – and he too wants to “get his,” no matter what the cost.