There is a distinction between Steem (the blockchain) and Steemit or dTube (which are websites that interface with the blockchain).
The teams that run Steemit and dTube can censor what is shown on their website. Indeed, anyone who has their copyrighted content shown without their permission on Steemit can write to the Steemit team and ultimately get that content removed from Steemit. They can equally choose to take down illegal material. Also they have opted to hide content that has a sufficient amount of downvotes from users.
However the content will still exist on Steem the blockchain. And someone else could create a "Steemit uncensored" website that shows everything, including content Steemit has blocked/ hidden for whatever reason.
Another distinction to make is that video files shown on dTube are not themselves stored on the Steem blockchain. They are stored on another (peer-to-peer) platform, IPFS.
So the videos themselves do not have the censorship resistance of the blockchain however they are hosted in a decentralised way. If a file contained illegal content, I believe there are ways that people running the nodes that host it can effectively blacklist it . If no-one seeds the file it won't be shown. However someone somewhere could seed it and make it available on IPFS. It's worth bearing in mind that there are costs associated with hosting IPFS files so the videos are not guaranteed to be hosted for all time, without further payment (I'm no expert in IPFS btw but that's my basic understanding).
From a Steem blockchain perspective, it hosts text, albeit some of that text may be links to media. So the question becomes whether text can be so egregious as to warrant censorship/ regulation - which would be virtually impossible on a decentralised blockchain, it would be like trying to censor the internet. If the issue is the media - then the best recourse would be to pursue those that host it (e.g. on IPFS) or those that show it (e.g. on a frontend interface like Steemit or dTube or Busy or whatever).
Okay, that answer was a little longer than I expected by I hope it helps. Welcome to Steemit and thanks for answer the important questions that many are bound to ask!