First of all: How do you know what goes through an animal's mind as it's in line to be killed? I'm also sure you realise that not every abattoir, particularly in third world countries or cultures where the animal has to be killed in a certain way, would treat their animals humanely. It's been a big deal in Australia recently that some of our cattle were being sold to Indonesian abattoirs where they would torture the animals for no reason before killing them.
Second: If someone was going to kill and eat you, even if you knew you weren't going to feel any fear or pain, would you be happy to let it happen? It's about more than mistreating animals for me, it's about basic respect for life.
I don't mean to sound preachy when I'm saying this, it's completely my opinion. You guys can do what you want. Just sharing my thoughts.
The fear and pain gives it extra flavor.