Yeah ... I know this is a quote conglomeration --- big deal (( fed case )) to the trivia - psuedo science cult FR freeks (( vs freeps )) !
There had been, and were at the time, many fatuous and overblown speculations on subjects such as the nature and origin of species, earth/cosmic history, and the like. Darwin didn't want to be classified with such dilletantes. He had a carefully constructed and sober case for his views, and the chance that it would be fairly considered was better if the initial presentation was "toned down".