How many serial killers who dismember and eat their victims have a mental illness?
How many mothers who kill their children (eg: Susan Smith, Andrea Yates) suffer from a mental illness?
How many school shooters suffer from depression, were bullied, and/or have some form of mental illness?
You can "say" mental illness should be on a case-by-case basis, but when a group of people exhibit similar traits, it should be safe to assume they probably have a mental illness. Especially when they repeat the same phrases or keywords.
Apotemnophilia - I was born in the wrong body. To fix this I need to remove a piece of my body.
Transsexual - I was born in the wrong body. To fix this I need to remove a piece of my body.
Not all serial killers eat the bodies of their victims. One of the most infamous, Jeffrey Dahmer: According to the Wiki article on him, Dahmer had a multitude of factors in his life that led to his behavior, not all of which were/are mental illnesses.
http://en.wikipedia.org/wiki/Jeffrey_Dahmer
You're welcome to look up other serial killers who've eaten the bodies of their victims on your own.
Both Yates suffered from forms of depression. See below for link to depression.
It's likely that school shooters (Columbine, New Haven, etc.) suffered from depression but depression has many causes: According to NIMH, depression is a medical issue with a combination of genetic, biological, environmental, and psychological factors.
http://www.nimh.nih.gov/health/topics/depression/index.shtml
You're welcome to look up more info on the individuals yourself.
Philia is a suffix and does not denote a mental illness. From the article: Suffixes with the common part -phil- (-phile, -philia, -phily, -philic) are used to specify some kind of attraction or affinity to something. They are antonymic to suffixes -phob-.
http://en.wikipedia.org/wiki/-phil-
Apotemnophilia can be associated with Body Integrity Identity Disorder but can exist on it's own.
http://en.wikipedia.org/wiki/Apotemnophilia
Transsexual:
http://en.wikipedia.org/wiki/Transsexual
You can say it's safe to
assume that groups of people exhibiting similar traits all have a mental illness but you would be wrong. Even a perusal of the information linked in this response shows that there are many factors involved in the specific examples you used.
I see at least three things wrong with the bolded statement: "assume", which I already pointed out; "probably", does not mean definitively; and "repeating the same phrases or words" which does not make the two groups the same.