How do you judge whether Descent of Man is a text that can change the public position, or too radical and not worth defending? If you only defend things that don't get a negative reaction, and anything contrary to the current dogma gets a negative reaction, you'll likely never get anywhere.

Also, the strength of the reaction against a non-conformist text is not really strongly correlated with the degree to which it's non-conformist. Dogmatics police small deviations precisely because they don't want an incremental strategy to work.