legalities, dark magic, and dark wizards

[stevemac]

No: HPFGUIDX 151153

stevemac:

 From reading some of the recent posts about DD and Parseltongue, I  
thought it was interesting that I did not have a clear distinction  
between these categories...

Although it is easy to get the general 'dark magic = bad'  
connotations, I'm really curious about what others have to say on  
where the definitions and dividing lines are. They seem very gray,  
and by some definitions I have read, HP has definitely used full- 
blown Dark Arts/Magic in the final scene with Snape in HBP - he knew  
that the purpose of the sectumsempra was to cause harm, and used it.

I'm just wondering where the boundries lie between illegal magic,  
dark magic, and dark wizard.

stevemac