Definition of soapboxer:
(n) :
A small platform, being or resembling a literal soapbox, on which a person stands in order to give an impromptu speech or espouse his or her views.
(n) :
(figuratively, often pejorative) A platform or outlet, such as a media platform, that a person uses to express his or her opinions.
(n) :
(derogatory, especially in phrases such as 'on/off one's soapbox') A figurative means of talking repeatedly or at length about one's opinions on one's pet topic.
(n) :
(loosely) The topic itself.
(n) :
(literally) A crate for packing soap.
(n) :
A soapbox car.