Step one, you get a group of people from a different forum to post about new topics, and vote consistently on them.

Step two, by doing that, you attempt to create a false consensus and make it seem like that opinion is popular and correct.

Step three, anyone who disagrees is piled on and removal is attempted via mod actions/etc if possible.

Step four, you collapse the forum once it's taken over and move on to the next one, in order to stop the people who disagree with you from forming effective resistance.

Notice it, call it out.