Is modern life a cause of mental illness?

I'm considering Hysteria and how this diagnosis has gone from endemic
prevalence to relative obscurity. One might suggest this was an
achievement of psychiatry and psychoanalysis or one might suggest that
this is due to a change in society.

My bias is the latter so I'll wander along that thought process.

The idea of split personality is falsely associated with the modern
diagnosis of schizophrenia. Split personality is still considered by
many as schizophrenia and by attachment of that label it's immediately
considered a pathological state.

And yet how many of us have different personalities. Perhaps these are
personalities that we control and are therefore different to a person
with dissociative identity disorder. Nonetheless one might suggest that
we don't look examine people's personality to look for signs of their
different personalities showing in every day life.

I'll give the example of lawyer. In the office they are one person. In
their private life they may be a very different person. In court they'll
be different. In their family life they may be different.

These are all areas where people have to play roles. They are roles
which people have to develop into. Not everyone is flexible and
malleable to easily fit into these different roles. Even for those that
are it takes time. The change make not always be what the individual is
suited to so there's a force applied to get them to develop the
personality or façade required for each of their roles.

Is this correct though? Is society forcing people to behave in ways
they're not meant to be like. It's as though people are required to
change to suit the task which is agreeable in the context of
productivity yet denies the human.

The flexibility of personality seems an important requisite of modern
life but perhaps this is something only few people can achieve. Actors
and actresses might excel at their ability to play these roles having
had the training to dissociate themselves from their external
presentation. Others may have higher levels of connectivity between
their inner self and outer presentation, for example the person who
wears their heart on their sleeve or the person with no poker face.

Our internal selves are forced to present ourselves differently in
different areas of life but this seems nonsensical to someone coming
from a perspective where society is built for the human race rather than
the other way around. People are forced to sheer themselves internally
to fit within their various roles, to wear the many "hats" (as De Bono
puts it) as is expected of a 'normal' human being. It's as though
society wants people to have multiple personalities as long as all the
personalities are under control yet vilifies those who don't have their
personalities under control.

And, as in my view happened to the majority of what was diagnosed as
hysteria, could a change in society offer a way to salve the souls of
those trapped in pain through society's requirement of controllable
multiple personalities and façades of characters we're asked to don to
work and play well?