I can't speak for anyone else, but as a Christian, it's really quite simple: any death that you help cause is a black mark on your soul. Maybe you can repent for it, someday. But it's not something that will just be let go when the day of reckoning comes.
Incidentally, I'd feel the same way about killing someone in self-defense.
What if avoiding causing a death instead results in thousands of deaths? Do you give yourself a moral high five and stick your head in the sand?
I thought accepting and believing in Jesus as Lord was all you needed to enter heaven?
John 6:40 (KJV) 40 And this is the will of him that sent me, that every one which seeth the Son, and believeth on him, may have everlasting life: and I will raise him up at the last day.