mental illness mostly just refers to what society doesn't like. [... ] These things are often induced through abuse or indoctrination

The modern criteria for mental illness was designed to be more closely related to how medicine sees illness. Like I said before, it is not arbitrary. Ironically you are using mental illness as an attack on something you don't like.

Mental illness has both a genetic and environmental component and usually show up around the 20s of a persons life. Religion can be taught, replaced, changed, abandoned at any age and at any point, there's no onset of when religious symptoms show up after being healthy.

It is, they assume normal is healthy. Normal is retarded.

Psychology doesn't make claim normal is healthy. Normal in psychology doesn't exist, psychologists are trained to help with the needs of a patient. They provide relief from bad coping habits and negative thought patterns (like saying your feel like trash). They train schizophrenics to cope with hallucinations and delusions, and help patients with medical compliance. Medicine that has been scientifically researched and tested for efficacy.

The reality of mental illness is complex and has many variables, it IS a broad subject

We are talking about if the definition of mental illness is broad not if the field is broad.

If deviancy is only mentally ill when it pertains to dysfunction then what's the point of even mentioning it?

Because mentally ill behaviors are deviant. People suffering from bipolar disorder have a tendency to end up regretting everything they do during a manic episode. During which they have such high impulsivity in which many end up cheating on their spouses, spending money they don't have, doing something illegal, getting in trouble with the law, etc. This abnormal impulsivity is temporary as part of the episode, and is one of the criteria for diagnosis.

These include social and professional challenges, so should being smarter than average be considered mental illness

No because intelligence doesn't have a pathology like religion. It's not deviancy by itself that determines whether something is a mental illness, it the combination of all the elements: deviancy + distress+ dysfunction = mental illness (also note that I am simplifying a lot here).

Those things are very mentally ill.

Why? What have you determined to mean by mentally ill that differs from the ones used by professionals?

Most geniuses struggle with those things, the problem is society not them.

There's is a correlation between intelligence and mental illness. If someone is struggling with those things, they should seek professional help. We live in a society where that is possible.

That implies that a disturbing number of humans need to believe in magic sky fairies just to refrain from killing themselves

That's not what it implies. Most of those studies point out that it's not necessarily the believes that are causing the effects, but the communities that are formed that contributes to the reduction.

People are conditioned into mental illness whether it is the socially acceptable kind or not

There's no way to condition someone into a mental illness. Even were many people in war might experience the same events, some people develop PTSD while others don't.

Schizophrenics and whatnot are usually abused or neglected in some way, or are genetically defective.

Not necessarily, triggers for schizophrenia are complicated being one of the most hereditary mental illness. Probable one of the most misunderstood mental illnesses as well. With all mental illnesses adversity while young can increase the occurrence of mental illness BUT it is not the cause of it. And as with all mental illnesses, it can be improved with proper treatment and medication.

Religion doesn't have a genetic factor, it is all social. Extremely dependent were you are born and raised.

do you not consider delusion and retardation to be mentally ill?

Retardation is a nerodevelopmental disorder. Anyone can become delusional: hoping your favorite team is going to win big despite the evidence, for example. Those type of delusion aren't pathological. Psychotic disorders on the other hand, when they become delusional they mark a change in behavior, a lot of times a very drastic one. Psychotic delusions also respond to antipsychotics while most "normal" delusion don't.

religion is delusional and retarded to the extent that I view religious people as subhuman apes.

You're not going to be very effective at changing someone's mind if that how you view people. Anyone can be indoctrinated into a religion, the social pressure in some groups is enormous. Personally I only view those people as ignorant and nothing less.