To what extent are our actions in virtual reality (by which I mean virtual representations of physical worlds, and not the Internet) subject to ethical criteria?

I can think of only two ways that your actions in virtual reality are "subject to ethical criteria" (i.e., are appropriate targets of ethical judgment). First, if they somehow have effects on real people (for instance, if you have virtual reality sex and your spouse finds out about it). Second, if your virtual reality actions shape your beliefs or character in ways that make you more likely to behave unethically in the real world. For instance, having virtual reality sex or killing virtual reality characters in a video game might make you more likely to cheat on your spouse or to behave violently in the real world. I say "might" because, as far as I know, the research on this is either non-existent or inconclusive (though I think there is some good evidence that children who play a lot of violent video games are more prone to violence).

This offers a nice example of how ethical theory depends in part on facts about our moral psychology. Virtue theory suggests that our ethical behavior depends on habits of thought, feeling, and action that we learn through practice. So this theory would predict that realistic virtual reality behavior would likely influence our real-world moral behavior, and hence we should be careful about what we do in virtual worlds. This view seems plausible to me. I'd suggest that we test it empirically... except if it's right we may be making people worse by getting them to pretend to be bad in a matrix world.

You might be interested in the study described here in which people "performed" the famous trolley dilemmas in virtual reality:

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