Again, retreading old, old ground, so I'll only be countering one thing:
He had absolutely no descision in it. He cannot be held responsible for his actions even if Jenova wasn't in control.
This is, quite possibly, the stupidest thing I ever heard and I think my IQ has been lowered just from reading it. Sephiroth had no choice in being implanted with Jenova cells before birth, but he made a very conscious decision to go on a killing spree when he found out the truth. This was not some "no other choice" situation. Finding out something shocking doesn't give anyone a license to kill. Sephiroth had two clear options: "murdering people" and "not murdering people". He chose the former, nothing and nobody forced it upon him. Such an idea is completely ridiculous.

Anyway, now that you've admitted you have no actual proof to back up your theory (and also said that you'd take your own clearly flawed "logic" before legitimate dialogue - i.e real evidence) it seems quite clear there is nothing left to debate. No proof = no truth, and I need no longer go over the same tired points. Good day.