It seems to me that there is some question of psychology here. 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. Presumably you are not worried about people who enjoy gunning down row upon row of zombies in a shooter. Now, it is permissible to question whether this whatever-it-is that makes people want to play the role of torturers is something we want to keep around in the human psyche; perhaps we'd like to self-edit it out. (Or perhaps not. I have no strong feeling either way.) But the point is that the difficulty doesn't lie in the roleplay, but in not recognising where roleplay ends and inflicting suffering on a real, conscious being begins. So to answer your question, I would work to explain to people that computer entities will eventually be conscious, and thus deserving of the same treatment we give other humans - yes, even if they look like just lines of code; and explaining the concept of Nonperson Predicates that shows why it's permissible to torture Sims but not ems. Then, for those few who would still insist on torturing ems, there is either law, or the social mechanisms that currently prevent people from torturing dogs even when it might not be strictly illegal.
It is probably not possible to avoid all em torture, just as we cannot avoid all torture of humans today. But with good education the problem needn't be worse.
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 ...
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.