Yes, they are but they kill humanity in inhumane ways.
It’s a mistake to simply label terrorists as “evil” or psychologically deranged – in fact, psychologists who have studied terrorist groups have found that terrorists tend to be stable individuals, not paranoid or delusional. What seems to make terrorists essentially different from others is their ability to “switch off” their sense of empathy in service to their beliefs and goals.
Empathy and compassion seem to be natural for human beings. It’s natural for us to feel for the sufferings of others, and to respond with a desire to alleviate their suffering. If you lack the ability to empathize, then it’s very likely that you could be diagnosed as a psychopath.
To become a terrorist means disengaging this natural empathy, so that a person can treat certain other human beings .. the members of the groups he feels he is fighting against …as objects, and kill them without remorse. It means seeing members of those groups as fundamentally “other” and refusing to connect with them. It is only a complete lack of empathy which makes it possible for one human being to behead another.
Terrorism is the symptom of a sick society; and like any competent doctor will tell you, the only way to get rid of a symptom is to treat the disease. Popping pain-killers will not cure you of the headache if it’s caused by a tumor in the brain. Just agonizing about how horrible the pain is will not make a whit of difference so far as the underlying tumor is concerned.