See, I personally find it hard to call things like Anorexia Nervosa an illness. I think that they are more a state of mind. This may sound strange, but hear me out.
The DSM-IV-TSR says that Anorexia Nervosa can be diagnosed if the following are true of the person:
1. Refusal to maintain body weight at or above a minimally normal weight for age and height (e.g., weight loss leading to maintenance of body weight less than 85% of that expected; or failure to make expected weight gain during period of growth, leading to body weight less than 85% of that expected).
2. Intense fear of gaining weight or becoming obese
3. Disturbance in the way in which one's body weight or shape is experienced, undue influence of body weight or shape on self-evaluation, or denial of the seriousness of the current low body weight.
4. The absence of at least three consecutive menstrual cycles (amenorrhea) in women who have had their first menstrual period but have not yet gone through menopause (postmenarcheal, premenopausal females).
If you'll notice, these all require some sort of conscious thought that is not caused by an abnormality in the brain's ability to function (with the exception of the 4th, but the 4th is just an effect of the lack of nutrition)
If you think about things like Psychopathy, they all have some physical problem with the brain's ability to function, often a problem with one of the neurotransmitter chemicals.
There are other "mental illnesses" such as Anorexia Nervosa, Post Traumatic Stress Syndrome, and Generalized Anxiety Disorder that occur with no direct physical symptoms. (Weight loss is not a direct symptom of Anorexia Nervosa, it's an effect of not eating which is caused by the mental symptoms of Anorexia Nervosa) All of these sorts of disorders are triggered by some stimulus that is purely psychological, and all of them can only be cured, so to speak, with other psychological stimuli (Note that they can be managed with medicines, but the medicines only work as long as they are taken, they do not cure the problem, just offset it) If you'll notice, for all of these types of disorders, the only cure (Defining cure as being a treatment that can have permanent restoring effects, even after treatment has ended) is therapy. Therapy, of course, is just a targeted set of psychological stimuli.
It is also important to note that the majority of the latter group of disorders did not exist if you go further back in history. Now, I do not mean that they went undiagnosed, but they simply didn't exist. Anorexia Nervosa, for example, was not a problem because being thin was not a good thing in anyone's eye at one point. Beyond that, the idea of needing to be good looking did not come from so many directions. Post Traumatic Stress Syndrome probably existed, but would not have been as wide spread, because the idea of respecting fellow man didn't exist, and many other events that are traumatic today either didn't happen then or were not traumatic then.
For these reasons, I find it odd that Anorexia Nervosa is often likened with illnesses like Schizophrenia when they are so fundamentally different.
Directly addressing the proposal of force-feeding anorexic patients, I was previously throwing around the idea of letting people choose for themselves. I am still inclined to stand by this position, because I do not feel that Anorexia Nervosa takes away a persons ability to make decisions in the same way that Psychopathy would. However, even if you do say that Anorexia Nervosa is something that should get a person sectioned, force-feeding would not be the smart thing to do with the patient once they are sectioned. It has been previously said that people will "get over" the humiliation involved. Anorexia Nervosa is primarily caused by humiliation with one's own body. While most people would not be affected so greatly by this humiliation, anorexics are, so it would not be a great move to humiliate them further, as it would be very likely to cause an entirely new disorder.
I still feel that Anorexia Nervosa is not something to be sectioned for, however if you feel that it is, force-feeding is still not the way to go.
As for the people saying that it is "a fact" that Anorexia Nervosa is an illness, the idea that you hold on to that so tightly is mind boggling. You have to understand that some facts are only facts because they cannot be false. An "illness" is something that is defined and understood only by humans. Therefore, if humans call something an illness, it's an illness. The fact that it is an illness doesn't mean jack-diddly, because it just as easily could not have been. It's like saying that it is a fact that one hour is sixty minutes. You are talking about two definitions that we created. The fact that one hour is sixty minutes is pointless. A better fact is to say that the earth takes a certain amount of time to travel around the sun. No matter what your frame of reference is in that case, that will always be true.
Back to Anorexia Nervosa, the only reason it is an illness is because we said it is. Playing sports could just as easily be considered an illness, because it is so risky. Even more specifically, let's go with the sports player who continues to play when they are knowingly injured. We ended up calling that brave, or determined, but it can be just as risky as Anorexia Nervosa. If sports were not a way to demonstrate toughness and resilience, then that sports player would surely be called mentally ill for what they do to themselves. Because fighting through an injury is considered to be strong by society, it is not an illness. Society has decided that, in this case, the ends justify the means.
If anyone wants to dispute the legitimacy of the sports player as an analogy, consider the football player who continues to play after repeated concussions. That person is not considered mentally ill, yet they are very clearly at a high risk, perhaps even higher than the anorexic, of dying or doing other permanent damage to themselves.