I agree, for the reasons you've stated as well as others. While I do think being able to properly label adult content is important, its better achieved through

I agree, for the reasons you've stated as well as others. While I do think being able to properly label adult content is important, its better achieved through a meta tag, the class attribute, or in the case of a link, the rel attribute. With the HTML5 and XHTML movements a primary focus has been on eliminating non-semantic tags like div and span. Its a noble pursuit, but I think in the witch-hunt to eliminate general purpose, non-semantic tags a monster has been created. When all elements must be semantic, we need many more to achieve the same goals. Microformats are an example of doing it the right way. Instead of creating new HTML elements to represent each concept, microformats use an existing, general purpose attribute (class) to convey meaning. I'm all for adding new elements when they make sense, but a NSFW element feels like a step backwards.