I just completed the writing of a paper on the dumbing down of language in cyberspace. My post search lead me to this cite. In answer to your question, I believe in a community we all have a responsibility to each other. The internet community is no different. However, I doubt I would be alarmed if I stumbled on that type of information online. I would most like make the assumption that that person is probably writing a paper on the subject. I believe our computer screens act as bullet proof vests that protect us from the emotional baggages of other internet users. If on the other hand I was walking on the street and found a note that indicate this type of danger to someone, I would feel the need to take it to the authorities. It becomes more person. Another point is that these issues only stand out in our minds if they are addressed in the media. For example, If the search term used indicated that that person was trying to find child pornography for example, because this issue is constantly being highlighted in the news, I would take note and yes, I would feel a responsibility to take it to the authorities.

My humble opinion.