I’ve heard this claim before that it is not possible for atheists to have “objective moral beliefs” because many moral claims are based on religious authority, which atheists do not believe in.
Thus atheists are subjectivists when it comes to morality: each atheist may disagree with the other about what is moral. Obviously this opens atheists up to problems of disagreements, with some who might believe very conventionally “immoral” things are acceptable for them.
This is not of course to say that atheists may not choose to live lives that are some what “moral” (moral, as is often defined by religions)
So, what’s the status of the idea of “objective morality” and atheism?
Animals aren’t “someone” and eating other animals is, and has been, part of the natural order of things since animals have existed.
I have been taught animals aren’t things, therefore they are not something but someone.
The relevant part is that they have their own conscious experience that you are negatively impacting by killing them, the same reason it is wrong to kill a human.
“The natural order of things” is not a guide for morality; lions rape each other, that is still immoral.