End of story.
The Punisher is a lone wolf. He listens to no authority, lets no one stand in his way. He rights the wrongs and does it with finality. If you are engaged in a crime, he will kill you. This is teenage male wish fulfillment at its finest.
The idea of doing harm to all the people who have done you wrong ... and then taking it further to make sure no wrong is ever done again is appealing. The notion that authority, be it law enforcement, your parents or school, cannot contain you is a fantasy second only to sex in a teenage boy's mind. When the Punisher steps into the fray he becomes symbolic of what every wronged teen boy has imagined at one time or another ... guilt-free, rampant vengeance. It's part of why he's so popular, and since teen boys grow up to be teen men, he remains popular.
If revenge were all the character had to offer, though, he would be soon relegated to second tier status, and that's being generous. Through the hands of various writers, however, Punisher has taken on something that goes beyond mere violent masturbation material. (Excluding, of course, those ill-conceived detours into the realm of angels and pseudo-Frankenstein monsters.) He has become an almost tragic figure. A twisted Christ. He wipes evil from the Earth, but is destined to do so alone (or with the help of a few select friends) and be alone. He has been resurrected (again, in those horrible storylines). He has attracted the ire of self-appointed protectors who find his methods too extreme and have punished him for it. Is he to be worshipped? Only by the psychotic, but there are plenty of readers who can understand and even sympathize with is actions.
There is something cathartic about ridding your world of evil. Not just locking it away with the hopes that he or she will be reformed. Sometimes your problems can only be solved by defenestration or massive explosions. Were you do to those things in real life, you would be hunted and most likely caught. You would have to hope a jury of your "peers" would understand that sometimes rapists have to be shot in the face. And you would hope they have pity on you. The Punisher has these concerns, but they don't matter much in the grand scheme of things. His titles sell well enough that readers know he will never truly be reformed or cancelled. He will live to kill another day ... once again brought back from the dead to show the world the error of its ways.
