I'd say that blocking the content doesn't always reinforce their beliefs. For a lot of people, reading something that is then blocked at a later date reinforces the belief that the information they consumed is not only true, but so true that it has to be censored by some authority, because it would threaten said authority's legitimacy.
As an example, imagine you think that the police are too violent, and you stumble upon police bodycam footage of a cop getting unnecessarily violent at a traffic stop. You bookmark the video, and then later when you try to tell people about it, the video has been taken down the police, for whatever reason. Wouldn't that reinforce your belief that police are too violent?
I know this isn't a perfect example, because a video of someone doing something is much different than an article making claims based on little to no evidence. But the reason some people's beliefs are reinforced by censorship is because they can't help but wonder if the people doing the censoring are trying to hide something.