In defense of Snape (from a Snape hater).

[Casey]

No: HPFGUIDX 134164

Pippin:
I don't think Dumbledore intended to die. I think he trusted that
Snape's AK would not be strong enough to kill him, and I do believe it 
wasn't. AK victims die with their eyes open and they simply collapse 
on the spot. They don't get blasted into the air. The curse failed,  
IMO, ,just as Harry's attempt to crucio Bella did, because Snape 
didn't really mean it. And what of the vow?

Casey replies:

A lot of this was from a discussion with WingedFigment on LJ.

I think Dumbledore told Snape during the argument that if push came to 
shove he wanted Snape to kill him instead of Draco. That he didn't 
want his death on Draco's soul. I think Snape out and out refused.

When Dumbledore drank the potion out of the well, he knew it was a 
poison, that's why he wanted to see Snape right away, to get the 
antidote. Instead there was a battle waging and he knew that he was 
going to die one way or another.

I think he stalled Draco until Snape showed up, and then begged him to 
kill him. Not only would Snape stay alive and continue to help the 
Order and Draco would remain untainted by murder, but there was 
another person that could have taken blame for Dumbledore's death, 
Harry. 

Harry force fed the potion to Dumbledore, which was why he was going 
to die anyway. How would Harry feel knowing that he murdered his 
mentor? The man most important in his life right then? It would have 
been too much of a burden and Dumbledore knew that.

So instead he begged Snape to kill him. Snape hated Dumbledore for 
asking that of him, and loathed himself for complying. Those feelings 
fed the curse that ended Dumbledores life.

Casey