The whole Season arc kind of bugged me this season really. In my opinion 'She was grieving and she was upset and she wasn't really herself' isn't a strong enough excuse to justify what she did and the fact that she commited murder. I think Warren deserved to die, yes, but it was not her place to carry out that sentence herself. As Buffy has said before, he was human, Tara died at the hands of a human, the laws of Buffy's world don't apply, it wasn't up to her whether he should die or not.
Yes, Willow WASN'T herself then, but just because she is mourning does not mean she can have a free reign to do what she likes. I think it's annoying that people were so quick to forgive Willow for what she did. I'm not even talking about Warren. She nearly killed Dawn, she practically tortured Giles, mentally hurt them all, messed with their minds and erased their memories, messed with Tara completely, left Buffy to die, and hurt Xander and it all was her fault. People like to sidestep around the fact that it was in fact all her fault in the end. She was being an idiot long before Tara died, that was just fuel to the fire. You can't say she should be forgiven because the magic had overcome her, when it was HER fault that she did magic in the first place. She was the one, her alone got hooked on magic. Just like any drug addict.
She was insecure, she needed a place to fit in, she found magic, she found her place in the group. She did a few spells, she found Tara, she found who she really was, she gained power and she was happy. She went too far, that was her price to pay. She knew what she was getting into with magic, she had been given many warnings by her friends the whole way along and she chose to ignore them. So I can't say I feel much sympathy for her at all really when it comes to her addiction. She messed up, her friends offered support, she shunned them and she hurt them and I wouldn't forgive so easily. Yes she is human and everyone makes mistakes and she regreted it, and deserves to be forgiven but I think she got cut a lot of slack because she was Willow, cute, adorable Willow. If it had been any other character in the show, except maybe Buffy herself and at a stretch Xander, they would not have accepted what she had done so easily. Do you think if it was Anya or Tara that all the gang would have been so understanding? I don't think so.
I think she went way too far over the entire season, and got let off way too lightly. I love the season, I love the concept of addiction and how Joss explores it, I just hate how the gang seem to have a kind of double standard when this happens and I think it's solely because she is Willow. She did wrong. They are no excuses, she should have payed the price a lot more than she seemed to.