(E) says, "People who harm others through impersonal means are no less culpable for their actions than are people who harm others in person."
(E) tells us that someone who harms others online is just as deserving of blame as someone who harms others in person. The problem with (E) is that it doesn't help justify the argument, as it doesn't give us information that education would help this problem. Thus, (E) is out.
(A) says, "Education about the ethical use of a tool increases one's sense of moral responsibility regarding its use."
We know from the stimulus that the big issue with the Internet is a lack of moral constraint. With (A), we know that education would increase one's sense of moral responsibility, which helps to justify the reasoning in the argument and the conclusion that steps should be taken to educate people about the ethical use of the Internet. Thus, (A) is the correct answer choice.
Does this make sense? Let us know if you have any other questions!