Moderation doesn't seem right either, though: the people who wanted to be part of those (toxic, terrible) communities had chosen to go there, and the only times they popped up in other communities was people linking to them as a sign of how terrible the people there are (counterproductive as a strategy).
Moderation implies curating an intermingling of user-generated comments so as to provide a super experience for the people reading those comments. There was no intermingling here.
I think a large part of the anger is that people on Reddit tend to recognize it's a patchwork of communities, each with distinct borders you can't cross accidentally, and they like it that way. In contrast, this decision is motivated by a desire to expand Reddit's appeal to new users and as an advertising platform, both of which rely on it having a good reputation to the outside world.
Say you post an article about the current state of socioeconomic affairs in the EU in /r/askscience. Your submission will be deleted, because /r/askscience's subject is not to host such articles. There is room elsewhere in Reddit for such an article.
Censorship is the suppression of speech, public communication or other information which may be considered objectionable, harmful, sensitive, politically incorrect or inconvenient as determined by governments, media outlets, authorities or other groups or institutions.[1]
"Censorship" implies suppressing free speech, which this is not. It's simply removing undesirable content from a privately-owned website.