"Just as I shall select my ship when I am about to go on a voyage, or my house when I propose to take a residence, so I shall choose my death when I am about to depart from life. Moreover, just as a long-drawn-out life does not necessarily mean a better one, so a long-drawn-out death necessarily means a worse one. There is no occasion when the soul should be humored more than at the moment of death. Let the soul depart as it feels itself impelled to go; whether it seeks the sword, or the halter, or some draught that attacks the veins, let it proceed and burst the bonds of its slavery. Every man ought to make his life acceptable to others besides himself, but his death to himself alone. The best form of death is the one we like. Men are foolish who reflect thus: 'One person will say that my conduct was not brave enough; another, that I was too headstrong; a third, that a particular kind of death would have betokened more spirit.' What you should really reflect is: 'I have under consideration a purpose with which the talk of men has no concern!' Your sole aim should be to escape from [disastrously ill] Fortune as speedily as possible; otherwise, there will be no lack of persons who will think ill of what you have done."
This made me think of arguments about others' methods when we personally may find them too painful or otherwise undesirable. There is never a lack of persons who will think ill of it!
But it also made me think of passive suicide methods, such as by train, cop, or traffic. It's this line in the quote above that points out to me the ethical consideration of life intersecting life in such instances, and why it's difficult to go along with and think well of passive methods in terms of morality or ethics:
"Every man ought to make his life acceptable to others besides himself, but his death to himself alone."
Seneca's talking about the Stoic ethic of considering one's responsibility to others alongside their own desires. In accomplishing death, no such consideration is required. However, if one is, at their last moment of life, interacting with and employing another at during an intersecting moment of the other's life in order to bring about that death, then it is no longer about making such a death acceptable only to the one pursing, enacting, and achieving it.