Eid-ul-Zuha is about the spirit of sacrifice

Although the slaughtering of innocent animals is heart-rending to many, according to Mufti Mukarram Ahmed, the Shahi Imam of Delhi's 17th century Fatehpuri Masjid, the sacrifice of animals too is a part of balance of nature.
http://ummid.com/news/2011/November/07.11.2011/about_eid_ul_adha.htm