About death curses
Let's speak about inflicting death with curses and all the bad decisions behind it.
What is a death curse?
A death curse is a type of a spell that inflicts death to its victim. This can be anything from a car accident to instant heart failure, it can be also as bad as a cancer. There are few infamous death curses like Pulsa diNura.
Pulsa diNura is a very strong Jewish curse in which angels of death (if I remember correctly) are called to prevent any God's forgiveness to reach the target, the target then dies because of his/her own sins. If curses were considered weapons, Pulsa diNura would be a nuke. It could also be considered an act of terrorism because it is usually abused against political figures, often for different ideologies.
Why people choose to use death curses?
People who tend to use death curses are usually insecure and emotionally unstable, thinking they can kill people remotely gives them some inner security and sense of power, that's why death curses are often chosen by "satanic" emotional teenagers, generally speaking majority of so called LHP groups are children and real and experienced practitioners are actually in minority (and they wouldn't curse so lightly).
Why death curses often don't work?
A death curse is a very serious thing that requires a killing intent, you must hate someone so much that when he would be near you right now you would kill him with bare hands. Thankfully most people are unable of such hate, else this would be a very sad place to live. Anyway, this also means death curses are used where you really want to kill some person that cannot be reached normally (living far away, well secured political figure, unknown rapist in the neighborhood, etc). It certainly cannot be used on a classmate sitting right next to you just because he broke your pencil and laughed at you that you dress like a bat.
Death curses usually have a reason, whether someone bullies you, make fun of you, or anything else. Question is why you want to go through the trouble to curse the person when a simple spell can be used to nullify just what you don't like, e.g for a bully to stop picking on you, your boss to stop making you work overtime, your political nemesis to stop thinking through his wallet, etc. This way you will also more likely get the desired result as it stems from your need and no killing intention is needed (in other words, this approach is good for non-psychopathic people).
Death curse between Magicians
I think you have heard stories of duels of Magicians and how a stronger will can beat the weaker will, about shielding and waiting for a right moment to hit to incapacitate the other guy. This all is more or less true regarding thaumaturgists, but when it comes to a theurgy, this is a completely different story. We are more or less a property of spirits we work with on a regular basis (the rapport works both ways), and the spirit, as any owner, gets angry if you try to damage its property. Spirits are also conscious and they talk to each other. I know I don't speak about this much, but I actually stopped doing any client work as my spirits forbid me to do few exorcisms, I was told to care about my own family and don't poke into problems of others.
So, what does happen when one theurgist try to curse another theurgist? Seemingly nothing, spirits make a deal and maybe let a lighter curse to pass through to make a point, if that teaches you not to mess with others, fine with that. But if you try some stronger curse, or even a death curse, spirits get really angry at you for trying to push them into some tacky spirit war and they might punish you, as well. Worst thing that can happen is that you ignore any warnings and if nothing seemingly happened, you try again. Spirits then might abandon you for your ignorance and then you suddenly find yourself without any protection and open for a counter-attack that can hit you in a full scale.
It is true that a stronger spirit might screw with lesser spirits, but don't also forget that each spirit has its own "homeland", so locally they can be strong but remotely there are some problems. For example if you tried to use a Voodoo lwa on me, you are likely to fail as voodoo spirits are very far from home here, on the other side my spirits are locals here, so they are way more accustomed to this environment and protection here.
So, we have learned that death curses are not really so bright idea to begin with, there are also alternatives: bully can stop mocking you, rapist can be arrested... or castrated, etc. We have also learned that spirits like their comfort zone and hate messing with other spirits and can punish you if you try to mess with other spirits or their "property".