Full Idea
Involuntary euthanasia can normally be ruled out, because it falls foul of the autonomy objection, and it is likely to have appalling side-effects.
Gist of Idea
Involuntary euthanasia is wrong because it violates autonomy, and it has appalling side-effects
Source
Jonathan Glover (Causing Death and Saving Lives [1977], §15.1)
Book Reference
Glover,Jonathan: 'Causing Death and Saving Lives' [Penguin 1982], p.191
A Reaction
The only defence of it is if the prospects are utterly horrible and the subject cannot grasp them. However, is this true of children or the very old. Paternalism may be appropriate, if the decider has reliably depressing knowledge?