If Rick wouldn't have killed Shane, he would have snapped and tried to kill him again. Maybe I'm just interpreting it wrong but I seen it as Rick thought it was the last straw and he had to kill Shane.
Rick gave Shane numerous opportunities to redeem himself at that point it was either Rick or Shane walking away. Not both. Rick did what he had to do..
I agree 100% that Rick had to kill Shane, but that doesn't mean it wasn't murder. Self-defense is when you or someone else is in mortal danger, not, 'oh it's cool because he'll probably just come back at me again'. Rick himself admitted that he just didn't want to deal with Shane anymore. I understand why he felt he had to do it, but let's call it what it is.
And yes, I defend Shane. I think people say 'but OMGZ he fugged his friends wife!' and he is crazy but as I said many, many pages ago in this thread, I don't feel like enough people look at things through Shane's eyes.
He tried his hardest to get Rick out of the hospital, but with people shooting and walkers all over, it just wasn't possible. He then protects his wife and child during the worst scenario imaginable. He then falls in love with Lori and treats Carl as his own. He is the leader of the group and his opinions and strategies for survival are both encouraged and accepted. He is what most men aspire to be. Protectors of their families, a leader, and respected. Then Rick comes back and gets Lori and Carl back, and then constantly puts the group in harms way and then completely disrespects Shane by constantly trying to boss him around. Shane and Rick pre-apocalypse were best friends, and partners. PARTNERS. Why does Rick think he is above Shane? He wasn't his superior on the force, and he's not now. He makes Shane constantly feel like less of a man, and most guys here will agree that nothing can make a man snap faster than someone trying to make you feel like less of a man. The group was Shane's and then Rick waltzes in and says my way or the highway? Then the icing on the cake is in Shane's final moments Lori comes up to him and, regardless of her naive female intentions, gives him just enough reason to think maybe she still cares about him, finally making him decide Rick has to go.
Shane has been living in this hellhole longer than Rick, and thus he snapped first. But look, mere hours after he killed Shane, Rick himself has snapped too, and will shortly be what Shane already was; a good and loyal man who is living in a world of survival of the fittest, not honor, being what gets your family to another sunrise.
People say how can you defend Shane?
I say how can you not?