Well, if I recall correctly, one of the first appearances of the Punisher was when he tried to off Spidey. Not very hero-like.
Sorry XTF, but I've got to go against you here. The guy was never a hero. He never saved children from the paths of out of control trucks. He stuck knives in bad people.
And the Punisher is anything but realistic. Spiderman cheating death hundreds of times a day is acceptable, the guy has superpowers, he isn't human. But the Punisher is human. It's almost impossible for me to take the Punisher seriously. What he does, how he does it, and the odds he faces in doing it are soooo ridiculous as to beggar belief. Spiderman is presented as a super powered being. It's a given that he survives all kinds of crap, that he takes on the worst and walks away from it. That's the advantage of being super powered. The Punisher is presented as a human being, yet we are supposed to accept the things he does, the things he takes on, and the things he walks away from. For a superhero to do these kind of things is believable, it's within the rules that have been created in this characters universe. But for a human to do these kind of things? Nope. not for one second. Calling the Punisher believable and realistic is like calling James Bond or Die Hard realistic. Spiderman is realistic within the rules and the world it has created. If Punisher was remotely realistic, then after the first five issues he would have been pushing up daisies.
Disclaimer: I'm not bad mouthing any particular writers or series' of Punisher. I admit I haven't read any of Ennis' run. My beef is with the Punisher in general.
So, there's my two cents. Well, more like $1074,56.