Parallel lines or crossing paths?

As a nerdy geeky type I often watch films. Recently I watched Terminator:Salvation and other then being unimpressed with the lack of general story the story that it actually contained had me thinking. During the course of the T1-4 films the characters develop an obsession with time travel. So a series of TT related incidents happen as follows:

• T-800 is sent back to kill Sarah Connor before she can give birth to John Connor.
• Future John Connor sends back Kyle Reese to save Sarah and become Johns Father.
• T-100 is sent back to kill 10 yr old John Connor.
• Future JC (not to be confused with the holy JC) sends back another T-800 to Kill the T-100
• T-X is sent back to kill the past/future generals of JCs army
• Future Johns wife sends T-850(model1) to save young JC and kill the T-X

Alot more happens in the films then that but to recap the 4th film Future John must find and save young kyle Reese who is being protected by a part human infiltrator Terminator. This amount of time travel starts getting confusing when you look at the paradoxes created. my favourite one being. Future John Saves Young KR then sends him back to save and bump SC and thus give birth to young JC. These paradoxes are easily explained if you take each film as an alternate reality, especially if you add the SC-Chronicles to the mix aswell. With JC falling in love with the Terminator that he sent back from the future to protect himself , played very nicely by Summer Glau.

so here I am drifting on the seas of confusion and I'm trying to scramble some sense out of all this but the main thing that bugs me is that Skynet , The main bad guy and super smart computer system that takes over the world with sentient robots and thus drives humanity to extinction, Is actually an idiot. They waste all this time sending things back and forth through time when one simple action would ensure ultimate victory.

Heres my theory : Future Skynet herein known as FS sends a message to Past Skynet (PS) not to send anything after john connor. the events would unfold as follows. Sarah Connor would never meet Kyle Reese as future JC would never send him back to save SC, thus SC would never know about the Terminators or Skynet and There would be no defence for the earth.

Endgame.