Political.
Given that historically the land (and lives) of many indigenous peoples was taken for grazing. My main reason for not eating animals is ethical, but almost as importantly it is important to make the distinction that this is an industry that has done and continues to do much damage to indigenous peoples.
The history of Native Americans is well known. The bison were exterminated, in part, to create and maintain a dominant “cattle culture” across the Great Plains and the West—and, unfortunately for Native Peoples and wildlife—it worked. http://www.buffalofieldcampaign.org/about-buffalo/buffalo-and-native-americans
Australian indigenous people suffered a similar fate. In the face of continuing resistance, and justifying their actions by a belief in the superiority of their civilisation, the colonisers pushed Aboriginal people off the fertile lands into controlled settlements. http://www.clc.org.au/articles/info/the-history-of-the-land-rights-act/
I am uncomfortable with people having been killed, rounded up, forced into settlement (including being converted to christianity) and being effectively banned from their traditional lands which became pastoral leases or even freehold land. All so cattle can be grazed.
That is why I intentionally added the word "historically" in the answer. Australian indigenous peoples are still trying to get their lands back.