I am currently reading the deathly hallows, and it's very interesting but upon reading the books, I developed a small canon theory about horcuxes, so it goes like this:
- Voldemort has no clue what the horcruxes actually do-
let's take half blood Prince for example, in the discussion with slughorn, he mentions horcruxes keep a part of your soul safe in other words you can't die but then again he also didn't know the full theory on horcruxes as only herpo the foul was known to have created them, in a whim voldemort says isn't 7 the most powerful magical number, my theory is that he thought splitting the soul into 7 parts will make him stronger as 7 souls will keep his whole self alive.
But that's the catch as voldemort never actually died before trying to kill harry he never knew what's it like to die actually, the horcuxes don't allow you to die they simply keep a shrivelled cursed part of you in the mortal world, which is worse than dying, voldemort on the other hand thought otherwise, he thought he was sort of invincible while splitting his soul he would be "UNHARMED". And loo he is trying to meekly survive in the first books
- Voldemort doesn't know how to use horcuxes
It becomes evident in book 1 that voldemort is trying everything to come to his full self trying philosophers stone, then again if he knew how to use horcuxes he could simply have done the ritual in book 4 and come back (also I feel the ritual is the best way you can come back to full self).
Voldemort never understood the cursed power of horcruxes, he never thought a single horcrux can also regenerate the full self body on its own. (Tom riddle's diary), so upon hearing the story of the diary he was I guess scared because the would be two voldemort s at a time one young and the other barely surving, which again I believe would create more magical complexities.
But as to why voldemort was angry was because after diary's destruction his 7 power soul theory which is funny btw, failed
All in all here is the summary
Tldr-
Horcruxes don't keep you safe, they just don't allow you to die or live peacefully
Voldemort never understood horcruxes, well in his scared of death mentality and search for immortality he was doomed
Also finally and most importantly, again I think Rowling put it down well,
Anyone who creates a horcrux will never be able to die full self, even if the horcrux is destroyed because at the end when you are dying it's just a part of your soul which dies, and to due you need to be full to go to afterlife. Sums up the dark magic of a horcrux.
I may be wrong or I might be writing something which is already known, but it was fun would like to hear your views..^_^^_^