Definition of soapbox:
(n) :
a crate for packing soap, or, by extension, any inexpensive crude platform raised above the surrounding level to give prominence to the person on it, especially when used for speeches; a talk about one's pet topic (or the topic itself,) especially when only tangentially relevant to an ongoing discussion
"the madman obtained a soapbox which he stood on at the corner of Broadway and Wall street, to shout out his prophesy of the end of the world."