In tournaments, the killer instinct is more obvious. There is money at stake, along with prestige. To an observer, the players' focus and attention is much more intense. The opponents may pass a few courteous words between themselves, but that is mere window dressing. The unspoken challenge is visible in their attitudes. Focus is on the table, not each other.
Some individuals feel somewhat uncomfortable with even the smallest bit of exposure to their primeval animalistic instincts. They will either avoid “desperate circumstances” or lose the match rather than awaken the inner beast. These players rarely advance their skills beyond a personal comfort level.
There are a few who have the strength of desire and the focused drive to do whatever it takes to compete at the higher skill levels. These individuals must possess the full-fledged killer instinct. During the match no prisoners are taken. Each duel is to the (figurative) death, and no mercy or kindness is offered or intended.
In competitions, the desires of these individuals are obvious to any observer. Players with killer instincts are not involved in conversations, jokes, or comments during the match. All of their focus is on drawing deep within themselves to bring their competitive spirit to the forefront.
The question is - how much of the feral animal do you want to experience? How much competitive spirit do you have (or want to have)? When playing in a friendly group, intensive competitive attitudes are out of place. This focus will be a bit uncomfortable for your opponents. It may get to the point where you need to find another group to play. Unfortunately, you will have outgrown your old friends.
This may occur when you experience an epiphany of competitive understanding while your friends do not. That is when you have to hunt down tougher opponents. You can still have friendly competitions with your friends, but you have to give spots (handicaps) to keep the games interesting. The problem with developing a killer instinct is that you have to keep it fed.
Regardless of where you are now in the grand competitive scheme of your pool career and where you will be in the future, enjoy yourself. The game is the game at whatever levels of "killer instinct" you currently apply. Even if you only like the friendly competitiveness of the game among friends, things may change your mind later and learn to appreciate your inner animal.
As your skills improve, the game stays interesting only as long as you are playing opponents at and slightly above your level. Against weaker players, you will actually lose your skills, simply because you don’t have to work at winning. Against far superior players, there is no enjoyment in watching them have fun while you only get up to rack the balls. Good luck and shoot straight.