Youtube: Censors youtubers, documented in so many cases. It also gives "authoritarian news" a heavier weight in the algorithm. Removes comments with "communist bandits" in Chinese.
Twitter: Seriously bans people if they say the wrong pronoun
Reddit: A few people controls the majority of big subreddits, bans people with conservative views outright. Bans people that upvote stuff that they don't like. The have removed, banned hundreds of subreddits and users in the last few months. While they have chinese owners.
Facebook: Surprisingly the best of the bunch when it comes to serving every viewpoint imo. But they have had huge privacy implications just so many times.
But even so, I am very torn on the subject. The best thing would probably to force these companies not to censor/ban/remove people based on opinions. But the best thing for the world would most likely for these social media sites to not exist in the first place.
Personally I think social media sucks but I think most people are not ready to live without it either.