According to this article by Ven. Dhammavuddho Thero:
Majjhima Nikaya 55 ..... The Buddha denied this, adding “Jivaka, I say that there are three instances in which meat should not be eaten: when it is seen, heard, or suspected (that the living being has been specifically slaughtered for oneself) … I say that there are three instances in which meat may be eaten: when it is not seen, heard, or suspected (that the living being has been specifically slaughtered for oneself).”
And another quote from the same source:
Anguttara Nikaya 8.12 ..... This is one of the discourses which clearly shows that the Buddha and his monks ate meat. Also, we see that meat from an animal that is already dead when it is purchased is allowed to be used, but not if the animal is alive.
In summary from the above and various sources:
- It is wrong to kill or directly cause the killing of animals
- It is wrong to have a livelihood on the business of meat
- It is wrong to consume meat that is from an animal that is seen, heard or suspected to have been slaughtered specifically for you
- It is ok to purchase and consume meat from the market (already dead before you arrived at the market)
My thought is that although the last case is not wrong due to an individual not being the direct cause of the killing of the specific animal, the individual is still contributing to the general demand that drives the meat market i.e. encouraging the supply of meat by butchers. If there is no demand, then there would be no supply. Unlike a tiger killing its prey, a butcher only slaughters the animal if there would be purchasers who would buy its meat.
So, why is this not considered wrong by Buddhists?
EDIT: Preferably, according to the Theravada tradition.