The animal-rights movement, once considered a fringe political cause, has become a significant force in American culture, with advocacy groups claiming millions of members and public-opinion polls showing growing popular support for animal welfare. Activists argue that all creatures have a right to live free from pain and exploitation and that humans should give animals' needs greater consideration. Some believe animals should have legal rights similar to those accorded humans, and many oppose eating meat or using animal products of any kind. The issue pits animal-rights activists against modern, large-scale agricultural and livestock producers, biomedical researchers, hunters and the operators of some zoos and wildlife parks. Critics of the movement say it ignores meaningful differences between humans and animals, including the higher thought processes and ability to make moral choices that distinguish the human race from the animal kingdom. They reject the notions that animals should have rights and that people have no right to use animals for the benefit of humankind.