Shane is basically a Zombie

There is a reason why the Walking Dead is viewed so highly: because the pilot episode set the tone for relationships, zombies, emotion, death and everything in between so well, that people could not sit back and ignore it without some sort of lingering thoughts. I myself like the comic more; it's the true zombie apocalypse bible. The television show has done it justice, even with the addition of characters not in the comic, overplayed and downplayed scenarios and a larger abundance of zombies and mutilated humans. 

Shane was and still is my main focus on the comic. I'm not exactly sure how I feel about him, although he is vital throughout the first and second seasons and the first comic and spoiler alert, subsequent comics for he's the baby daddy to Lori's second child. In the comic, Shane and Rick seem to act and feel more like good friends than they do in the show, and maybe that is due to minute details being overplayed in the show to cause more tension early on. Rick's character seems to be genuinely happy around Shane until the final moments when Carl shoots him, but in the show, they are more portrayed as 'partners', more formal and business like than neighborly fiends who share a squad car. In the first episode, they eat together and discuss women, an easy topic that fill the space whilst waiting for a call, but it shows Shane's true intentions and feelings for Lori. He is pining for his best friends girl and Rick is stupidly oblivious to it so much that if "Jesse's Girl" by Rick Springfield came on, he still wouldn't pick it up.

So why do people either hate or love Shane? Why is there no in between? He's only looking out for what's best for the group and Lori, which is a noble thing to do, apocalypse or not. I think the show overplays him being crazy and recklessly in love with his best friends wife, but that could also be attributed to him being killed off so soon in the first comic, which is a shame. 

Is Carl justified in killing Shane at the end of the first comic?

If Shane was still alive, do you think he and Rick would've had to actually fight over Lori or would it be more like the show with a slow waning of interest?