if farm animals were slaughtered in the most humane and painless of ways
This sounds like a juxtaposition to me. You cannot slaughter a healthy animal in a humane way. "Slaughter" excludes "humane". I'm not a vegan/vegetarian but it seems to me like this idea that if we just raised happy healthy animals and found a way to kill it nicely then eating meat would be ethically ok. We don't need to eat meat anymore. Any killing of an animal to make it into food is unnecessary and could be avoided. I think it is important that we meat eaters really internalize this. Every time we eat meat we caused absolutely unnecessary suffering for a quick moment of pleasure.