One thought I have in reading this thread is that the terms "fight" and "liking" need to be defined, as they mean different things to different people in the martial arts. For example, a martial artist may greatly enjoy watching or participating in a rule-controlled sparring match but would be abhorred by the brutality of any number of real-life violent conflicts, particularly those that involve maiming or killing.
Among our human needs is a need to use our bodies physically. Unfortunately, modern lifestyles are, on average, far too inactive to meet this need. And, while all of us experience the hormonal cascade (e.g., adrenalin, cortisol) of our fight-flight-freeze response quite frequently to perceived threats that do not actually endanger us in modern life (e.g., a frustrating workplace conflict related to the management of a project), our cultural training often prohibits our engaging in the immediate and intense physical exertion that would burn off those stress hormones. Taekwondo (and other martial arts) offers generally well-mannered people the delayed chance to engage in that intense physical exertion. The resulting improvement in how we feel after a good sparring match can quite naturally leave us with the sense that we "like fighting." And, as others have commented, many of us value knowing how to defend ourselves and take pride in our increasing skill to do so. Of course, there are also practitioners whose life experiences have contributed to high levels of aggression and/or who become addicted to the adrenalin of an actually dangerous fight and/or who have been culturally indoctrinated to like violence by repeat exposure to violence in the media or who have been psychologically damaged to pathologically like violence from growing up in a profoundly abusive environment, and so on. So, there can be what I would consider both healthy and unhealthy "liking" of "fighting." I think this is why traditional Taekwondo schools emphasize the philosophy underlying the art: it protects the practitioner (and society) from the effects of an unhealthy liking of fighting. Given the strong role of culture in the experience of and expression of aggression, and given anthropological studies of peaceful indigenous societies, I think there's more going on than just innate biology.