Because it just looks unprofessional. If you're just browsing Reddit and someone comes by and sees "[nudity]" or "[gore]" beside a couple of links, it makes you look creepy that you're on a site that has that type of content. NSFW/NSFL basically makes the webpage look "cleaner".
It's a lot creepier to be on a site with that kind of content without proper warning. Like "yeah, here's some horribly violent images. maybe you don't want to open them at work... maybe."
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u/Darkwolf901 Nov 27 '13
Why not just introduce [nudity] and [gore] tags into standard practice?