I never said he was a hero, nor that he was infallible, but I also feel that, though he's made mistakes, he isn't "the devil" as Jesse put it. Jessie's just as bad. Walt didn't kill Drew Sharpe, but his death put them in a situation where there wasn't really any other option. Jesse helped, as did Mike; they were the clean-up crew, and, as harsh as it may be, Drew Sharpe was collateral damage.
Is it a horrible act? Absolutely. However, you can't tell me that Walt's a bad, bad, bad, bad man and Jesse's not just because Jesse manifests his "feelings" by throwing money out the window and getting high. I guess what I'm saying is that all people are wired differently. Walt might whistle at work the next day, but that doesn't mean he doesn't feel anything.
It's the same as grief. Some people might be weepers; bawling their eyes out for everyone to see, and some people may not even be phased by something, only to let it stay bottled up inside. Drew Sharpe is the only real thing that I can give you. Those guys in the prison? They knew what they were signing up for. Fring? Mike? Same deal. I might be able to see Gale, but, even then, self-preservation. The same could also be said for Sharpe. Walt didn't pull the trigger, nor did he even order it, but, when it came down to "disposal," it was self-preservation.
I guess my biggest thing is this: is it a sin to embrace your human instincts? You and I will never be in these sort of situations (hopefully), but what if we were? Is it really wrong to value the skin on your back?