What would Snape have to do....

[bimbledor]

No: HPFGUIDX 138564

<big snip>

Doddie:
>> If Snape can dupe Voldemort...why not DD?!?!?

CathyD:
> Very true. But Dumbledore has a reason to trust Snape. A very 
> good reason and more than just the waffle he told Harry. And 
> it is obvious, to me at least, that Voldemort does not trust 
> anyone, not even Snape.

bimbledor here:

Hello, thanks for the interesting back-and-forth! I agree with 
Cathy, but of course, the fact that we're all pretty divided on 
this is IMO evidence of what a good writer JKR is.  

Here's my reasoning on why DD trusts Snape: 
the absolute, incontrovertible reason someone could be trusted to 
be anti-Voldemort would be that they are capable of love, that they 
love.
I think DD must, at some point, have become convinced of that part 
of Snape's character, whether through Snape's motives for deeds or
because Snape confessed to loving someone dearly (back to Lily?) or
because DD has seen this ability to love in Snape's memories through
the Pensieve.  If Snape truly has loved or loves, he wouldn't be
capable of AKing or of being a DE, just as HP finds himself 
incapable of doing the Unforgiveable Curses. 

ASIDE:(this of course lends credence to those who think that Snape
performed the AK knowing DD wouldn't die, either by not having the
intention, or by trusting DD's telling him it would be OK because it
wouldn't work....BTW, has anyone else noted that DD repeats the same
words Narcissa does in Ch 2, p. 33 <"...Severus...please"> with the
same number of "..."s? And in the same pleading tone of voice?  I 
took this as DD's way of reminding Snape of what was at stake, just 
as he reminds others of what they've promised. I also find it very 
difficult to imagine DD 'pleading' for anything, but not difficult 
to imagine him imitating a memory of Snape's)

I think it's the same reason DD knows Draco can't kill: Draco,
arrogant and cruel as he can be, cares deeply about his family.  It 
is his love and fear for them that is now driving him to complete
Voldemort's task, and it may have been a desire for fatherly love 
and admiration that initiated his agreement with V, rather than a 
pure desire for power. But that same ability to love stands in the 
way of his killing DD, in the way of Draco's tearing apart his own 
soul and becoming subject to the power of V. 

canon: pg. 511, HBP, US ed. - <"You are protected, in short, by your
ability to love!" said DD loudly. "The only protection that can
possibly work against the lure of power like Voldemort's!">

Only DEs and Voldemort are shown as having no love in their lives: 
the contrast between Narcissa (who doesn't appear to be a DE) and
Bellatrix in their reaction to offering up a son to the Dark Lord
couldn't be clearer. DEs and V lack this greater power. 

Any thoughts about this theory are welcome!

bimbledor, who believes in the complexity Snape