This is not so different to any other question of law, especially law in cyberspace. Can I stop people gambling online? It depends who I am and what measures I allow myself to use. If I am the state, and I ban computers from my territory, there's no more online gambling because there's no more online anything. If I believe it's a human right for people to spend their money as they wish, I am left only with appeals to reason and similar soft measures. If I allow myself to use physical coercion but intend to coexist with the Internet, then it's the usual situation with respect to cybercrime, or with respect to crime in general: there's a persistent underworld, and steady employment for law enforcement, and busts, confiscations, and court cases are just an ongoing fact of life.
You may be looking for answers to this problem which don't involve the state. Well, there are various software and hardware measures which are possible. You can make an upload physically un-copyable. You can give the upload an internal interface to its experience which renders it immune to coercion - all a hostile party can do is delete it. (Such measures seem to require that how the upload's defenses work is heavily obfuscated, at the level of source code.)
But of course, people who just want to torture and kill may be able to get copies of vulnerable minds from somewhere, or may even be able to generate them according to recipes. There's still a third class of solution, apart from 'the state' and 'technical security', and that is to change human nature itself. One would expect a lot of that to be happening anyway, in a society with the capacity for mind uploading. Also, this third solution naturally mingles with the first - sadists who enjoy their sadism aren't just going to volunteer for barbarectomies, and even ordinary people would feel some fear at the prospect of psychosurgically-induced pacifism, as it threatens to make them the prey of others who still have their vicious side intact.
The recent novel by Iain M. Banks, Surface Detail, is about a galactic war intended to shut down "hells" created by unfortunate civilizations which believe in technologically creating the afterlife of punishment that they believed in during their superstitious eras. One issue is that no-one knows where the hells are physically located, or what physical medium is hosting them.
I'd be curious about anything, governmental or not, which even vaguely resembles a solution.
On the torture vs. eye specks scale, the risks to ems strike me as not needing a lot of exponents.
Nevfgbv ol Jnygre Wba Jvyyvnzf has a similar situation to Surface Detail. The possibility of a hell planet isn't revealed till halfway through the book, so I've rot13ed the author and title. However, the book is a classic of transhumanism if you ignore the administrative problems.
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.