The Punisher's roots lie in Mack Bolan, aka, The Executioner, the hugely popular men's fantasy line. People who equate The Punisher with Taxi Driver because of spins later writers put on the character are missing the point of what he was created to be; Boland is someone that readers are supposed to like and root for and so too was Frank Castle. They are supposed to, at least to some extent, imagine themselves in the places of Boland or Castle. Gerry Conway literally said that he created The Punisher because he liked The Executioner and wanted to use a similar character in Marvel. He was going to call him The Assassin, but they changed the name because from the get-go, they wanted him to ultimately become a hero and that name didn't seem appropriate to that.
Some earlier Punisher writers that picked up the ball from Conway, like J.M. Dematteis, emphasized Punisher's psychological issues (such as during his 'Trial of the Punisher' storyline in Spiderman), but the fact is that the character was intended from the start to sympathetic, if edgy, and to act as if people are misappropriating him by wearing his logo or relating to him is to misunderstand what the character is supposed to be in the first place.
Gerry Conway went further when he created The Black Spider, who was willing to kill innocents in order to get at the drug dealers he targeted, but The Punisher himself was, from the beginning, intended to be a popular character that sold comics, just like his paperback counterpart and predecessor. If his creators didn't want people to admire him, then they wouldn't have imbued him with the same near-superhuman level of skill that Boland shares with him or kept him from doing truly reprehensible things like the Black Spider. Physically, The Punisher represents the pinnacle of male physical performance and of course, he also does things that many men wish they could do or even want to do. He's not nearly as morally flawed as Homer's Achilles, but look at how many people have admired Achilles down through the ages and attempted to identify with him, despite his flaws. That's an inevitable byproduct of making a character a paragon of physical prowess.
Basically, as great a character as he was, he was created for popular consumption, just like Mack Boland. And I don't think it is fair to get mad at people for identifying with him in some way, wearing merchandise based on him, etc., when that is exactly what his creators wanted people to do.