Greenpeace is against GMOs, but some argue that it helped alleviate the hunger problem in developed countries through improved yields. Is advocating against genetically modified seeds anti-science? Is there a consensus in the academic community on the matter?
If someone were to argue that GMOs do not exist or that some particular method which has been devised in a scientific manner to create GMO species does not exist or does not work, that would be arguing against the scientific method - which is one way to interpret "arguing against science".
If someone were to argue that use of GMOs leads to increased negative health outcomes, and makes this argument based on data gathered in a manner consistent with scientific method, this is not "arguing against science" - it is using science.
If someone were to argue that it is better to have some people get sick because of pesticide use so that other people don't starve to death - or the reverse - this is neither using science nor arguing against science. The same is true if someone argues that it is wrong to grant patents on particular genetic sequences. These are both examples of taking an ethical position, something upon which science is largely silent.
Greenpeace is clearly not anti-science; they are not opposed to scientific practices such as research and publishing. Their 2015 report on pesticides which includes over 150 reference citations, many of which refer to peer-reviewed scientific journals. Using references to scientific papers to construct an argument is the modus operandi of the scientist.
Disagreement among scientists doesn't mean anyone is anti-science. Scientists do not agree about everything all the time, but rather they build on shared research to create a deeper, more nuanced understanding of the world around us.
Being anti-science means having the belief that science cannot reliably provide the understanding that it claims to provide. You will know an anti-scientist not from their citations and research, but from the absence thereof.