Not breaking the first precept vs. developing compassion In Theravada, we have established that eating meat does not break the first precept in many Buddhism SE questions (for example, this question and other questions linked in its comments).

However, beyond not breaking the first precept, could vegetarianism be used as a practice of developing compassion (karuna) and being compassionate?

Or does the practice of compassion require direct intention and direct action in allaying the sufferings of others, and indirect means are not relevant?

Bhikkhu Khantipalo defined compassion (karuna) here as:


  Compassion (karuna) is taking note of the sufferings of other beings
  in the world. It overcomes callous indifference to the plight of
  suffering beings, human or otherwise. Likewise, it must be reflected
  in one's life by a willingness to go out of one's way to give aid
  where possible, and to help those in distress. It has the advantage of
  reducing one's selfishness by understanding others' sorrows. It is
  Lord Buddha's medicine for cruelty, for how can one harm others when
  one has seen how much they have to suffer already? It has also two
  enemies: the "near" one is mere grief; while its "far" enemy is
  cruelty.
Compassion is a wholesome quality, but compassion cannot take you to Nibbana. We use the practice of compassion to counter cruelty in the mind. But the goal of Buddhism is not about dedicating your life to the cultivation of compassion. If that is the case, you will have nothing else to do in life other than looking for beings in misery and trying to help them. How can you even eat, drink, wear clothes if all your actions are dedicated to compassion? There are always beings who do not have food, water etc. You should give all your food to them and starve to death yourself, if compassion is all that you should cultivate. 

Vegetarian food production causes much killing as well. So why not starve to death to save any possible loss of life? This kind of thinking comes from Jainism. Buddhism does not fall into these extremes. The goal of Buddhism is the end of suffering and there are other more important qualities that one must cultivate to achieve that. Being vegetarian is not one of them.