One of the better self help books I've read described good mental health as a willingness to engage in reality (M Scott Peck, The Road Less Travelled, well worth a read if you haven't). That description always stuck with me. It is a much better definition of truthfulness and deception than the one most of us carrying around about lying. For most people, lying is binary. You either are or you aren't. But that doesn't capture the nuances of evading looking at something you should be looking at, allowing someone to think something that they think without correcting them, etc. These lead to poor mental health, for both people involved in avoiding looking squarely at reality.
Under this definition no one is perfectly truthful. We all engage in some form of self-deception, some looking away at something troubling, and we are all also foolish to some extent, not having wisdom. If we look squarely at, for example, the suffering of children, we may feel like we are being truthful in our ability to take in difficult realities, but we are not wise about how our own actions continents away contribute to their suffering. Without that wisdom we are still far from the truth.
Pursuing reality and wisdom is the basis of truth, and someone engaging in sock-puppeting is at the basis of every interaction not engaging in truthfulness, is damaging their own mental health, and is participating in eroding the mental health of everyone they engage with. Even if they pose a question or situation that they think could happen in the real world (but is not) and people give sincere answers - it is not reality, not truth, and is destructive.
It's most destructive to themselves. I have seen the obvious cases of someone coming on like the LtCommander guy but the current case of posting false stories, engaging with whomever will come along (and more often lately with oneself) and then posting another when the engagement dies down, reminds me of a child who bursts into the play of other children, tries to direct it, gets a shot of gleefulness when the other kids go along for a bit, and then tries to console themselves by continuing to play solo after the others drift away.
The beauty of SI is the ability to read deeply into the experience of someone who is in the middle of one of the worst struggles of their life, to see how they describe it, to see how they manage it, and to be able to offer a compassionate ear and your own perspective. None of that is happening when there is lying from the outset. I suppose the best thing from the current rampant case of sock-puppeting is that people dedicated to the truth will have the chance to gain some wisdom. Which we all need.