"Mentally incompetent" means that someone is unable to make their own decisions. Someone who can navigate society well enough to support themselves is not generally considered mentally incompetent. Since plenty of people have "chopped off their dicks" and continued to navigate society well enough to support themselves, I think calling them all mentally incompetent is a bit of a stretch.
Kind of agree, but it does hinge on how you look at "incompetent." Define it as, "Keeping your stuff together and not bothering anyone else," and yup, you've nailed it. Define it as that plus, "and also do yourself no irreparable harm," and not so much. Courts have often taken that second step due to old age dementia, mental retardation, disability due to TBI, etc. IOW, when it does not involve chopping off a limb or dangly bits.
What ought not be in question is that these folks who chop off perfectly healthy bits and organs (be it genetalia, limbs, whatever) are
mentally ill. That requires zero moral calculation, merely Darwinian reasoning. Where morality and ethics come in are folks who make it easier for these mentally ill folks to maim and mutilate themselves. Those sort are no better than scum who take advantage of the elderly, the retarded, and children.
The sad fact is that most folks who go through with maiming/mutilating themselves are no happier than before. Their mental state has not improved, yet now they are irreversibly harmed. Antidepressants have a better efficacy rate helping these folks than going the choppy route.
Furthermore, I don't think we (as a society) should bother quiet so much with the "danger to themselves" part. It's one thing to go after someone who is a danger to others, but if the only person getting hurt is the person doing the hurting, well, than, that's their business. Feel free to offer them help/assistance on your own time, but you don't have the right to force help on them anymore than they have the right to force their BS on you.
Not as simple as that.
Would this policy of non-intervention apply to children(1)? Left alone, many end up hurting themselves, mostly in ways out of sight of the rest of us. The street urchins of Dickensian England and places like Brazil come to mind.
How about adults...with the mental capacity of children?
How about adults with adult mental mental capacity, but it is twisted by mental illness?
I am in agreement that much/most of this ought to be done by private charity, especially after ending the welfare state. But private charity has not the authority to act when the child/child-minded adult/mentally ill adult is unwilling.
Do we let our mentally ill neighbor cut off their arm with a chainsaw on their front lawn or do we act to prevent it even if they might not appreciate our act? Do we let the suicidal teen jump off the bridge to their death in the river below? Heck, most folk would be against letting a cat or dog, though lack of cognitive capacity, jump/fall off a bridge. And that letting such happen when one of us might prevent it as morally reprehensible. Should we value human life less than that of the aforementioned cat or dog?
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Obviously, much of the above is rhetorical and not meant to be addressed by BSL point by point. I think it does show the libertarian, non-interventionist approach is fraught with difficulties when dealing with children, the mentally ill, or otherwise mentally incompetent.
(1) Libertarian solutions break down many times when pushed up against the reality of children and foreign aggressors. We can mock the "What about the children?" crowd, but it is a question that needs answering as children have not the mental capacity of adults.