Unless you want to commit to the position that people with mental illness should just deal with "the body they are genetically and biologically predisposed to" (have we abandoned that as a metric that is useful yet? You appear to have jumped to an entirely different set of criteria for what is important), you should probably reassess your argument.
Again, there is a huge difference between physical diseases that can lead to death, and mental problems.
Saying I "abandoned" my argument is incredibly foolish. As for mental illnesses, yes, I entirely agree they are a thing, but...
Here are some other things that are "mental issue[s] that make[] people feel bad":
Anxiety
Depression
Bipolar Disorder
Schizophrenia
Paranoid Schizophrenia
Obsessive Compulsive Disorder
Post-traumatic Stress Disorder
All of these mental issues should be treated, but they should be treated through medication and therapy, so that they can return to a correct state of mind, or at least learn how to live with their issues.
Not by maiming themselves.