Discourse.org is 3rd party software.
Their official response:
https://meta.discourse.org/t/should-down-voting-be-core-functionality-in-discourse/40/6
https://meta.discourse.org/t/should-down-voting-be-core-functionality-in-discourse/40/21
https://meta.discourse.org/t/should-down-voting-be-core-functionality-in-discourse/40/30
https://meta.discourse.org/t/should-down-voting-be-core-functionality-in-discourse/40/37