fantastic post, mateHi there, hope you don't mind if I respond to this even though I'm not the OP you quoted.
In the name of transparency, I don't think (nor think there is evidence to the contrary) that anything is "inherently" bad. I don't believe any deity decreed to us any set of universal rights and wrongs.
I will state that your comparison of a lion eating something and not feeling remorse is not an apt one. First of all, lions are/may be obligate carnivores, in that their health will severely deteriorate without meat consumption. They evolved almost solely to function from meat, which is absolutely not the same as humans as our capacity for diet variety is leagues beyond that of a carnivore. Secondly, you are assuming a cognition environment of parity between lions and humans. Other animals certainly are smarter than we use to think, but there is currently no evidence to assert that a lion has the kind of mental workings necessary to reflect on the grander scheme of things and change his behavior as a result. Humans simply have the larger brains, and functioning grey matter volume seem to coordinate strongly with higher levels of self-awareness and reflection. It seems disingenuous to level the playing field here and expect the same kind of social/cognitive behavioral moderation to other animals.
I rarely will try and argue for veganism from the angle of moral duty due to my already stated thoughts on morality, so no. I just don't think other animals may even have the capacity to make the dietary/moral decision.
And you're right, ethics isn't really convincing at all outside of predefined goals, unless you're a theist. There are many other arguments for why veganism/greatly reduced animal consumption is objectively better than the alternative (objectively better when goals are defined, such as less resource use and less degradation of the planet), but that is hardly about extending the messy tangle of moral agency to other animals.
As for myself, I have chosen to model my behaviors around reducing suffering on sentient beings that can experience it, and try to maximize their welfare. Animals are sentient, and abusing them for taste falls clearly outside of my moral goals. Following this in return makes me feel good, but I think philosophical egoism/versions of hedonism is what drives nearly everything, anyways. Carbon that came alive just wants to feel good...