This is one of the few things I feel very strongly about. For me the killing of any sim is just wrong. I remember when ghosts were first introduced into TS4 and the forum was full of threads on ways to murder them. There was even a thread on how to get a ghost baby :( I wrote my own thread at the time, partly in jest, to complain about the situation and was horrified to discover how blood thirsty a lot of simmers really are.
For TS4 it is not entirely the simmers fault but the fact if you want a ghost of a certain type the game forces you to create your own. You do however have a choice about going along with what the game is making you do or resisting.
Back in October 2014 we formed a society for the protection of abused sims and the education of simmers. Perhaps it is time to resurrect the society :) The joke went on so long we were even planning bake sales, coffee mornings and a Christmas Carol concert.
Obviously how each of us play is a personal thing and there is no right or wrong way. It is also obvious this is video violence and in no way comparable to real life but even so some do feel an emotional attachment to their sims and would hate to see them harmed.