Yes, we've been doing it since the age of time, why stop now. Again, i'll bring up horses (at least we eat cows), what purpose do these animals serve in this day and age. None, except for amusement! If we're not being amused by these animals, I think we should kill them all, give Sally Struthers the remains, and be on with our lives. Remember, horses fart and therefore, contribute in the ozone layer problem. We can at least eliminate that percentage.
At last a straight answer.
But I think you're confused between (1) us killing & eating animals, (2) domesticating some of them for our own ends (companionship, food, sport), and (3) inflicting pain for our pleasure (eg rodeos, cock fights, bear baiting).
It's Number 3 I find absolutely unjustifiable. And cruelty/inflicting pain should not occur in (1) and (2).
And by the way, the gases emitted in horses' farts (and cows, deer, us etc) do NOT affect the ozone layer. These gases are "greenhouse gases", and as such are implicated in global warming.