Snape and AK curse

[Cindy]

No: HPFGUIDX 136146

Maybe this has been addressed already (I have been having a heck of a 
time catching up on the posts as I just finished reading HBP).

Snape used the AK curse on DD.  Why?  DD was near death, slipping 
along the tower, with no wand.  All Snape had to do was use a spell 
to fling him off the tower.  It is very unlikely someone could 
survive such a fall, much less one in DD's condition.  Why *that* 
particular curse?

Snape used an unforgivable curse.  Even if he is on the good side, he 
will most likely face prison for using that particular curse, if he 
survives and the good side wins.  Prison was the one thing he kept 
mentioning in Chp. 2 that he was afraid to face.  He has now doomed 
himself to such a fate.  The only reason I can think of is that he 
didn't care, because he actually *is* working for Voldemort.  

Snape does not strike me as a noble person in any way.  His character 
flaws have been pointed out in other posts, and I agree with what has 
been said.  I think the conversation/argument with DD was about Snape 
continuing to act as a spy.  He was afraid of Voldemort because 
Voldemort was becoming too powerful, and I think he may have been 
giving DD some excuse why he wanted out.  I think Snape *is* a 
coward; someone who follows the winning side.

Any comments?

Cindy