Raksasa means someone who causes harm, thus violating the principle of ahimsa (nonviolence.) This is a serious offence and is evil karma.
It is a general term applied to anyone of physically very violent nature. Sometimes though people have used the term patronimically, such as in the case of Ravana.
In many cases raksasas were cannibalistic. Cannibalism itself is a violent act, and hence, is considered a raksasa act. Even in Tibetan texts, one can find mention of cannibalistic raksasas. Padmasavbhava is described having taken the form of a turquoise cuckoo bird to subdue the cannibalistic raksasas ("slar lho nub srin-po'i kha gnon du g.yu bya khu-byug tu sprul nas gshegs-so.")
- P. 123 The oral tradition from Zhang-Zhung: an introduction to the Bonpo Dzogchen teachings of the oral tradition from Zhang-Zhung known as the Zhang-Zhung snyan-rgyud John Myrdhin Reynolds