With many domestic violence cases as well as nearly all cases that involve relationships, often the abused is subverted into thinking that they're at fault and deserve the beating.
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Hence not pressing charges is very much tell tale signs of phsycological trauma. The abused at this point is not in a rational state of mind to make any such decision. Thus again the state stepping in to press charges is again in protection of the abused's bodily right to privacy.
Now as for suicide, this to me is very grey. If it were some guy at the end of the line giving up on life cowardly that again is a sign of mental illness. Yes again the state intervenes.
However, in assisted suicides where the patient is terminally ill and has no chance of recovery whatsoever, yet must indure the tortures of chemo and radio therapy (cancer patients), thier state of mind is very clear and it's much more humane to allow them to die with dignity. Also it need be noted that in such cases the person's state of mind is very clear.