Why Fret About Voldemort Considering Riddle?

[Louis Badalament]

No: HPFGUIDX 106005


Alright, here's something I don't understand...

   In Book 5, Harry feels guilty about the possibility that he'll 
kill Voldemort;

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"It was very hard to believe as he sat here that his life must 
include, or end in, murder..."

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But my question is... why?  Why does he even *feel* this guilt?  
Remember book 2?  He killed Tom Riddle easily enough.  He was, in 
fact, rather proud of the accomplishment, even years later...

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"WHO SAVED THE PHILOSOPHER'S STONE?  WHO GOT RID OF RIDDLE?"  

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No one, no where, in any the books, has ever suggested that ending 
Riddle's strange quasi-life was the slightest bit dishonorable.  
True... Riddle was something of a ghost (a 'memory' for all you 
nitpickers,) but Voldermort's not exactly a human being either, no 
matter whether we're speaking figuratively or literally, either.  

My question, then, stands as such: why can't Harry, at that pivotal 
moment when he's finally faced with Voldemort for the ultimate Big 
Showdown just treat the matter as though he's facing an older, 
uglier Tom Riddle, (which he is), and just do away with him, as you 
or I would do away with any cockroach - free of guilt?  Voldemort 
certainly isn't worth any prickle  of shame - except in regards of 
failure to act.   

-  Louis Badalament 

P.S.:  Harry also didn't seem to have any qualms about ending 
Bellatrix Lestrange's life, either;

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'SHE KILLED SIRIUS!' bellowed Harry. 'SHE KILLED HIM, I'LL KILL HER!'
And he was off, scrambling up the stone benches...

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No sympathy for the one who killed his godfather, and yet Harry 
feels regrets about killing the one who murdered his father and 
mother?  It's all very weird to me.