Scientists in a particular field acknowledge the limitations of their field. Dawkins makes an effort to utilize his field as an explanatory framework for things that, in my opinion, are not part of his field. His efforts, along with those of other scientists, don't really break new ground as such, but come to justify opinions that have existed for a while,e.g., humans are naturally selfish.
The gene-centered view of evolution very much did
break new ground when it was first pursued by certain prominent biologists and popularized by Dawkins. "Humans are naturally selfish" is a mischaracterization of Dawkins' views, as well. Have you read the Selfish Gene? His view is that genes are ultimately vehicles that "care" only about their own replication. In that sense, he calls them "selfish." But selfish genes don't necessarily make selfish people. In fact, he's devoted lengthy discussions in many of his works to explain just how altruistic behavior can arise from "selfish" genes--the exact opposite of what you're saying he and others have done. As far as him directly commenting on things outside of biology that he thinks the selfish gene theory has implications for, I don't see a big problem with that. The vast majority of his work deals directly with evolutionary theory and nothing else. As for the small portion that doesn't deal directly in biology: When a scientist thinks their work has implications outside of its directly implicated field of study, I would say they're allowed to speculate on what those implications are just as anyone else is also allowed to (granted that they acknowlege its speculative character, which Dawkins does).