I think discussing things directly related to DEI for a company could be things like hiring practices, marketing materials, etc. that relate to the business.

General discussion about politics (or sensitive topics) in a company's forums, using company resources just isn't going to have good or relevant outcomes. If you're friends with coworkers, sure discuss away in DM or SMS or whatever external social media. Obviously people that were at basecamp strongly disagreed but there is a point there that political opinions, on any side, can have detrimental effects at work and isn't relevant to the work. Its unfortunate, but that is where we are in US society.