You are right. We have always proved that we are capable of using any technology for good and bad. It really comes down to the motives and agenda of people involved and I agree that this particular tool can easily be used to wipe off the memory of an entire population especially by a government. I wonder if they already have it and have used it before.
It certainly is dark!
I believe the times when this would actually be a good thing are VERY rare. Like I said it shouldn't be a matter of just wanting to erase memories. Those negative memories and learning to deal with them are important. The rare cases would be in cases where it is debilitating, or a person without a doubt is going to commit suicide if it remains. Things like that.
Yet like I said that is pretty rare. I consider any other use of this tool to be a very dark thing.
You are right. Negative experiences are equally important for life as the positive ones.