because there are legitimate uses of pre tags

some monks us them to create small ascii art sigs.

Other monks use them when raw data, or the output of a script -- which they don't want to put in code blocks because it's not code, it shouldnt' be included in the code download

Generating a warning if someone submits text with a pre tag containing lines longer then N characters is one thing, but it would be a travesty to flat out reject the tag just because some people don't know how to use it in a non-obtrusive way.

PS: regecting pre tags doesn't really do anthing about long sequences of   tags...