Three of the most common reasons for locking a thread (individual posts can be deleted but not "locked") are:
1. The thread started out with a prohibited topic (unions, politics, religion, which way up should a 120V 3 prong receptacle be mounted, etc.) and rather than removing the thread we lock it, with or without a comment.
2. The thread started out OK but drifted into a prohibited topic.
3. The thread was allowed and useful, but even after the requested answer was given the comments end up in a useless repetetive argument or wander totally off the starting topic.
Censorship is not in and of itself objectionable. In these cases, content restrictions have been publicly stated in the Forum rules and need to be uniformly enforced, whether or not we as individuals have a position on the prohibited topic. Censorship based on one position on a particular issue is more likely to be objectionable, and we try to avoid that.
Some of the prohibitions, including profanity and obscenity, are set by the owner of the Forum, and that is his privilege as the donor of this service in the first place.