Respectfully, you are the one who appears to be arguing in a pretty logically inconsistent manner, and even if I don't believe you entered this conversation in bad faith, I have to take issue with the whole "I don't need to explain why I'm right because I'm right" tone.
You start off by implying that they somehow only care about this situation because they have it out for the particular person who was accused, or something to that effect. Sorry, but I can't see how this is anything but a strawman. How did you come the conclusion that they "care about the names"? Why make a point of this otherwise?
Further, you framed this as a philosophical discussion, where you (by your own account) arrived to an opinion about this discussion from your base (utilitarian or similar) philosophical principles (i.e. "whether it benefits more people than it hurts").
However, you later clarify that "what the action is" is also one of your base principles, and it apparently implies that stealing is bad. You did say "illegal" instead of "bad", which is quite strange, since the accusation being made here is "spreading malware", which is also illegal pretty much everywhere. If this was your concern, why even bring up utilitarianism and all that other stuff? Why make suddenly conditional on an innocent person being negatively impacted?
If we disregard that interpretation, from an outside perspective, "what the action is" is so vague in the way that you have defined it, to the point that it can seemingly mean literally anything depending on your actual underlying opinion of the matter. I.e. it seems like your utilitarian-like principle actually doesn't have much bearing on your decisions or opinions, since it can always be trumped by the earlier clause. At least that looks to have been the result for every example listed in this discussion. What other conclusion is anyone supposed to make here?
The slippery slope fallacy doesn't really apply here. They're just taking your self-declared code of ethics and deriving possible moral decisions from it that match your criteria. This is literally the singular point of having a code of ethics. If you aren't willing to take the decisions that flow from it, you aren't really conforming to the code of ethics, are you now?
Meanwhile, a slippery slope fallacy is when you use the fact that someone took a certain small decision to assert that they must also necessarily take some series of increasingly extreme decisions that are in a similar vein. An important distinction is that you are, in effect, assuming their code of ethics based on one decision, and using that to infer what further decisions they will make.
In the first case, no one had to assume what your ethics were, since you told everyone your code of ethics (or at least, an outline of it), they just took it to its logical conclusion.