is there always a tendency to confuse punishment with revenge?

i agree with the author. Like the author had mentioned, "we often confuse punishing a criminal with revenge. Although the two are closely related, they have a difference."

"punishment is - or should be- a penalty imposed for violating the law, and is usually handed down by some authority."
"revenge on the other hand, is inflicting punishment, but usually by groups or individuals who do not have the authority to punish; it is generally the result of hatred rather than justice."

The difference would be that punishment is by some authority but revenge is not.
"the problem is that many times, even those allowed by the law to punish, do so out of vengeance." for example, the jury could judge a crime base on their own morals and not base on the law, thus sometimes, making the punishment more severe, turning it into vengeance.

"again, a crime can be so horrid that revenge is on everyone's mind and, as noted, this is understandable." for example, an eye for an eye. "how much effort we pour into hurting somebody else usually depends on how much hurt has been done to us. under such circumstances, we feel justified in saying that the person who had injured us got what he or she deserved." for example, when someone committed murder, we could punish the person by imprisoning the person. However, killing the murderer could be on some people's mind as some would want to exact vengeance.

Thus punishment and revenge can be easily confused as they are almost the same where there is the inflicting of punishment and the only difference would be that revenge is inflicting of punishment without an authority and it is linked more to one's feelings. Since everyone has feelings, punishment and revenge could be easily confused.