Okay, here are my thoughts strictly on topic (according to what the title says, because I didn't read back the entire thread).
If you wanna view the big picture without going into details, then humans, too, are technically animals; mammals, primates to be exact, and just like other animals, we are omnivorous. There're herbivores, carnivores... We're just a circle of life. Carnivorous animals eat each other too, and they don't think about whether they're right or wrong, it's just survival of the fittest. The only actual difference between us and them is the development level of our brains, which leads us to being the ones who overthink stuff like this. If we go to the sub-topics about cruelty/experiments on/against animals, of course the opinions can get a lot more shaded, and both sides can have truth to their opinions (like pro/con vegetarianism), but whether we simply have a "right" to kill and eat or not...? Yeah, we do. As much as they do, to do the same to us, because there are some species that would, given the chance - we're just better prepared, more evolved.