Those who enjoy torturing Sims do so, I think, because they know that there is no conscious being who suffers; so it is not real torture, it's roleplay.
While this is probably true to a large extent, there are plenty of cases of people abusing weaker beings they fully well know are conscious. Just look at the number of cases of animal abuse, child abuse and spousal violence filed, and remember that for every reported case there are likely several which go unreported. Heck, see almost any of the reports of the conditions in which factory farm animals are commonly kept. See also various reports of prison violence, police / hired guards abusing their authority, common treatments of prisoners of war, et cetera. Don't forget various cults using emotional or physical violence to maintain obedience among their followers. That's not even mentioning the various cases that are considered extreme even in Western society, e.g. serial murderers who torture their victims first.
Now take into account that there are probably plenty of people with leanings towards abusive behavior, who nonetheless abstain from it because they're too afraid of the social consequences. Then think of a scenario where anyone can run ems on their desktop computer and there's essentially no risk of ever getting caught. Furthermore, the risk of maltreatment grows dramatically if one can think of their victim as non-human and therefore not deserving of moral treatment. If your victim is an em and you're not, thinking like that isn't exactly hard.
Ems will make torture cheaper, just as the Internet made pornography cheaper, and so there will probably be more of it, yes. I am trying to suggest that the problem is not overwhelming; that the elasticity at the relevant margin is small, as it were, and can be further lessened by the outreach that we ought to be doing anyway.
When I was reading The Seven Biggest Dick Moves in the History of Gaming, I was struck by the number of people who are strongly motivated to cause misery to others [1], apparently for its own sake. I think the default assumption here is that the primary risk to ems is from errors in programming an AI, but cruelty from other ems, from silicon minds closely based on humans but not ems (is there a convenient term for this?) and from just plain organic humans strikes me as extremely likely.
We're talking about a species where a significant number of people feel better when they torture Sims. I don't think torturing Sims is of any moral importance, but it serves as an indicator about what people like to do. I also wonder how good a simulation has to be before torturing it does matter.
I find it hard to imagine a system where it's easy to upload people which has security so good that torturing copies wouldn't be feasible, but maybe I'm missing something.
[1] The article was also very funny. I point this out only because I feel a possibly excessive need to reassure readers that I have normal reactions.