I agree, and I don’t agree 
Flagging is a system tool available on this forum so, in of itself, I agree that it is not censorship.
Where I disagree is that what is important is how that flagging tool is used:
- If it is used to flag (and subsequently hide) a post that clearly breaks a forum rule (e.g. the repeated use of bad or offensive language, offensive name calling directed at the poster, etc) then it is clearly not censorship but a legitimate use of the tool
- If it is used to flag (and subsequently hide) a post because the person doing the flagging (a) doesn’t agree with the opinion expressed in the post, or (b) feels his/her opinion is of a higher value or is the only one that ‘counts’, or (c) doesn’t like the poster, or (e) something similar, then it clearly is censorship
In the thread concerned a lot of posts that were flagged and subsequently hidden fell into the second category, and not the first. So as @tomdi has suggested, better education as to how to behave and use this forum is a good start.