[Mistwraith]

There are some circumstances when parents do not deserve your respect or your love (abuse etc).

But thats the point, if the parent or parents respected and loved the child, then most of the time the child will respect and love the parent or parents.

When this happens its not duty that guides to aid the parent or parents in their years of need.

Some parent or parents do not want this, they are people too, and should have their wants and feelings respected, however there are some points at which the child is not the best person to care for him/her/them (altzheimers, parkinsons, etc) and profesional care after a point in time is the best for all concerned.

And .. after all .. there are nice people and nasty people in this world, people you love and people you hate, you will automatically love and care for them if thats the way you are.There are also selfish people who take and not return.
Its not duty, its personal human nature, and that cannot be changed or forced.