The crux of the matter (and potential controversy) is not about sex differences in plants or C. elegans. Most biologists I've met who study algae or polar bears usually limit their expert opinion on those species. It's really about transposing such knowledge to humans, where we don't have that level of bottom-up insight for a variety of reasons ranging from "humans are complicated", "most of what works in other species doesn't work in humans" (see: 99% of drug trials) to "you can't just open up people's brains to see what they're made of".