A lot of people I know who really have a blast started out with that worry, sometimes very validly. Most of them developed a greater awareness of where the line between fun and fight lay within them by trying out and sticking with the game. I started out as a bit of a loose cannon in a group that was more about violence than fun and it wasn't a problem for a long time. Being a nice guy, however, I changed my opinion of violence vs fun after I seriously injured somebody for the first time.
I went hunting for a more safety-conscious Field and discovered that the majority of these groups have a number of measures to help players enjoy their adrenaline without hospitalizing each other.
1) Equipment: Foam weapons are built along two major lines of thought. Either use hard foam weapons that will survive rough use (and wear armor) or design soft foam weapons that are significantly difficult to injure anyone with. Safety equipment (Cup, goggles, braces, bit) is always recommended, though rarely employed.
2) Etiquette: Some targets, such as the head and groin area, are considered off limits by most groups. Other dangerous actions such as body checking, tripping, and grabbing are also prohibited by most groups, giving the game a feeling closer to tag-meets-dodgeball than that of a fist fight. Those groups which allow such actions usually have regulations and trainers to help interested players "go there" and not to the hospital.
3) Degree of Contact Rating: There are only 2 degrees, Full Contact and Light Contact. Groups will identify as one or the other even when they are aiming for a grey area. Full Contact means that the players involved want to fight as hard and fast as they can while continuing for several hours. Light Contact means that the players get their game on, but with safety held as more important than "going all out." In a full contact group getting hurt happens, that's why such groups usually have waivers. Light Contact fields very clearly feel like a sport and not a fight, making it easier to get your game on without going into serious fight mode.
4) Community: Safe violence is an oxymoron, making it work takes skill. Skill comes from experience. Getting used to getting hit without getting hurt is what allows your defensive instincts to accept that you aren't actually in a fight, that your game is in more danger than your health. After that your combat instincts work for your mind instead of replacing it. That takes time and most people who have been through it recognize it. New fighters are usually welcomed and given a sparring partner who can explain the rules and help bring them up to speed.
That you care enough not to want to hurt someone and think you might enjoy it enough to hurt someone by getting into it too much tells me that you would probably not only love it but be pretty good at it after a while, likely one of the best in whatever group you join... eventually. Each thing in its own time. Macid, If you ever get the opportunity I suggest giving it a go. That one sentence you gave was full of potential...