Oh, I wasn't talking about that kind of censorship. I just meant how majority will use all means available (ordinarily - downwotes, in some cases as far as reports for stuff like instigation, trolling, etc., and almost always social pressure of vocal faction on the media of choice).
Case study: try going on Reddit and posting an unpopular opinion. It will get buried under a pile of dislikes and will never see the light of day. Your karma will take hit too. You may even get reported, depending on how bad is your study subreddit is.
People really don't like opinions that contradict the "accepted" opinion of their platform. And the "accepted" opinion is usually determined rather early on in the life cycle of that platform/community, and from that point begins the process of selection: people with "correct" opinions are welcomed, accepted and encouraged to stay and participate in "positive discussion", while people with "incorrect" opinions are made feel unwelcome, marginalized (unsurprisingly, since any "wrong" opinions are not allowed to gather any significant following in said community/resource) and ultimately leave and don't come back. Now, if we move to a platform that's not about just 1 thing, it gets more complex - there may be more topics that require you to have a "correct" opinion. And that's where we get to the censorship. While what I am about to describe may not be an explicit form of censorship, it nevertheless is limiting how freely people can express what they think. Say, your opinion aligns with what's established as "correct", but a topic comes up where you don't agree to the popular opinion. Most of the people will just either stay quiet, or reluctantly agreed with the majority because now there is a good amount of social pressure on them. On platforms like Twitter such social pressure might go beyond the internet and spill over into personal life - for example it may get you fired (which I am using purely as an example of it going too far, it's unlikely to happen over an opinion about some video game, or is it?).
Of course the degree of severity of what I described varies, and often you will find some people still going against the majority, but these results will always be biased in favor of platforms dominant faction. It's somewhat of a vicious cycle - these communities do their best to attract people who agree and chase off people who don't, therefore there is always majority that agrees and because there is always a majority that agrees it's hard for unpopular opinions to gain any friction, therefore people with unpopular opinions stay quiet or leave, etc.
While this is not explicit censorship, it achieves the same goal: keeps some of the people quiet either through social pressure or via technical means such as downvoting, reporting, feed display algorithms that hide controversial topics, etc..
Also as you could have noticed I didn't mention the actual owners of said platforms. They may or may not have some indirect influence via search algorithms and feed personalization, but all of it is the work of people who use the platform as users, sometimes user appointed moderators and such.
Point is: social platforms tend to degrade into echo chambers where any "incorrect" opinions are not welcome. So "most people on Twitter" is a poor indication of anything - asking Twitter or similar echo chambers about anything is just that - yelling your questions into an echo chamber.