If you're going to try and present unbiased facts as opposed to personal opinions, you can't approach slaughter as being inherently abusive.
Please don't let your ideals get in the way of real research. If you're not being honest with yourself you're only going to look for things that agree with your own position, which will give only a slanted view of the issues.
There are some abusive practices that can and do happen, but slaughter itself isn't the culprit. Dead is dead and death is never pretty, no matter whether it's from a bolt to the brain or by injected poison from a vet.
I do wish you luck with your project, but as I said, research all the facts, not just the ones that support your personal opinions.