Sometimes I feel guilty, sometimes not. Depends on if I like the sim or not.
Last Weekend I killed a female sim (mother of 4 children) for the Story I write.
But hey, somehow her fault. She had an affair with the Butler, married him while being pregnant with the 4th child from her lifepartner. The Butler became a Vampire then and he used his wife as a Food-source. I needed her to disappear for the continuation of my Story. I could not let her live, not even as an unplayed household.
So, No guilt in this case :)
But I saved the child and returned it to its biological father. The Girl did not deserved to live with her Vampire-stepfather. She lives happily with her three sisters and Brothers and with her half-sister and half-brother and does not remember her mother.