/r/collapse and /r/futurology are two forums on the popular website Reddit.  In February, 2017, they held a debate online.

At the time of the debate:

/r/collapse had about 40,000 members:

"Discussion and articles of interest related to the potential collapse of global civilization. In the context of this subreddit, collapse means a social and technological upheaval that results in a far more simplified society in terms of social order, technology, economy, and interdependencies, with an inability to rebuild within centuries or millennia."

and /r/futurology about 11 million:

"A subreddit devoted to the field of Future(s) Studies and evidence-based speculation about the development of humanity, technology, and civilization."

(Descriptions retrieved March 14, 2017.)

The debate between /r/collapse and /r/futurology: Debate - Does human history demonstrate a trend towards the collapse of civilization or the beginning of a united planetary civilization?