Why are they harmful? Are you saying you didn't learn a single thing while you were there? Redditors helped me greatly. Reddit was simply the platform through which we discussed incredible ideas and life tips, and I literally found and made friendships on there that have lasted since 2014+. Additionally, I learned a fair bit about CSS upfront as a mod of various small subs.
If you really think "any form of corporate social media is harmful" then I have to question how you were using it.