That Ahimsa (Non-injury) is the supreme virtue is no doubt true.
But merely professing it by word of mouth is worse than useless; merely refraining from killing animals, as for example, not taking fish or meat, is not Ahimsa. True non-injury can only be practiced when God is seen in all beings, that is, when the Self is realized.
The very nature of living necessarily involves at every moment, whether knowingly or unknowingly, destruction of or injury to the lives of countless beings, visible and invisible.
The Yogis practise austerities by living upon milk, because it is a purely Sattvic
food. But to obtain that milk the calf which has its birthright to the whole of its mother’s milk, has to be deprived of a part of its natural food. Is this not an act of injury or cruelty?
But the more one can live without consciously injuring or harming others, so much the better. However, by the habitual practice of real non-injury, one develops love for all beings, the little ego or selfishness disappears, and no distinction is felt between friend and foe. Consequently the heart is purified, and in the pure heart, God is fully reflected.
Swami Virajananda – a Monk of Sri Ramakrishna Order
Source - Towards the Goal Supreme, p.134-135