I actually cancel it more due to our user base, than to the problem of having it in the queue. (In fact, I thought I locked this thread). The problem I see is that new users will continue to join the site and not understand how things work here. However, while some people post positive and helpful things, many people respond ridiculous comments like "Ban this user" or "Burn him alive for submitting this" (Ok, slight exaggeration, I know, but it gets the point across.) Additionally, these comments can reach 2-3 pages - whereas many serious submissions barely make 1 page of comments. I'd rather not allow so much negative attention be focused on one submission, since it only takes a single comment to explain what the user did wrong. 30 people showing up to essentially
'mini-mod' a submission is NOT helpful.
(edit: I don't mind users contributing and helping explain what is wrong, in fact, many users are much better at it than I am. However, a torrent of users for umpteen pages isn't helpful.)
So, in clear and obvious rule breaking cases like this one, I cancel it, attempt my best explanation at what this site is about and why this submission doesn't follow our rules, cancel it, and lock the thread. This prevents new users from getting a torrent of negativity from our user base.