Question: Why liberate animals when going vegetarian is already practice of compassion?
Answer: This is a wonderful but passive means. In addition and contrast as an active means is liberation of animals about to be killed (especially for food).
Question: But animals are sometimes freed into wrong environments?
Answer: Most live animals openly on sale in markets will be killed in less than 24 hours – when bought to be cooked on the same day. Rather than letting them die in great fear and agony under the knife, it is always kinder to connect them to the Triple Gem, by sincere chanting and dedication of merits, and for release for natural living and dying in nature. Of course, we should look for ideal environments, but the truth is, there is never a perfect environment (even for humans), and even if they do not live long in an ideal place, they will definitely live longer than if they were brought to the chopping board. As such, it is already prolonging of life. Animal liberation is to save physical lives, but more importantly, to jumpstart spiritual lives.
On an additional note, it was advised by the Eighth Patriarch of the Pure Land Tradition Great Master Lianchi, that animal liberation is best done adhering to three guidelines – of not having a fixed time, location and kind of animals liberated. This effectively delinks supply from demand, by not presenting any form of predictability for sales. That said, even if there is some supply and demand link, the opportunity to link the animals to the Triple Gem is still precious.
Question: Okay. Back to vegetarianism, it is sometimes stretched to the ‘extreme’ as veganism in the name of Buddhism, though the Buddha was ‘not’ even a vegetarian. What do you think?
Answer: Vegetarianism was advocated by the Buddha as one of the Bodhisattva precepts in the Brahma Net Sutra, for how can we more effectively guide beings to the end of suffering if our consuming demands it, even if indirectly? Veganism is simply not consuming or using animal products such as meat, milk, cream, cheese, honey, leather, wool, silk… which are possible only due to extreme lifelong exploitation and eventual killing of these animals. As such, there is nothing extreme about being vegan. Here is more on why objection towards veganism (and vegetarianism) is the real extreme instead: http://thedailyenlightenment.
As the Mahayana sutras record, the Buddha gradually encouraged (as some are not ready straightaway) a clearly vegan lifestyle. This is stated by him unequivocally in the Surangama Sutra, which is upheld with great esteem by more dedicated Mahayana practitioners, as can be seen at the bottom of page 215 to 216 at http://www.buddhanet.net/pdf_