One-liners are NEVER acceptable unless they are a question asking for clarification. Otherwise, they are not constructive and they can't be built on to further the debate.
When dealing with unconstructive one-liners, our normal procedure is to either post a moderation note, if the member is new or not a frequent one-liner poster, or to outright remove the one-line post and PM the offending member. As the thread you are inquiring about, CR, was absolutely littered littered with one-liners, it would have been a daunting task to separate them out from the legitimate posts and therefore, had to be closed.
As we said in the closing note of that thread, anyone is free to start a similar debate in a few days/weeks. The real problem was with those who ruined the thread with one-liners, not us for closing it.
Hope that clarifies.