No, those tags are actually very useful. It's not the same as tagging something off-screen. These tags are only for instances where the area is completely visible, but the expected part is nowhere to be found. That IS remarkable, unusual, and should be tagged. And it is TWYS. You see a lack of nipples where they normally would be, that's a visible feature. Tagging really shouldn't run off of common assumptions anyways, because you may not need the tag to identify what you're looking at, but it still turns out useful for searching and blacklisting.

If something is reasonably expected to be included, then the fact it's missing is abnormal, unique, and should probably be tagged. No_dragon would make no sense because you can't reasonably expect one to always be there. But no_nipples IS unique because most of the time they are present and expected to be there, both in real life and in art.

If you want to argue about the theory of expectations and what's worth tagging, then it could be argued that it makes more sense to tag when they're missing than it does to tag when they're there, because missing nipples is the exception. Actually drawn nipples is far less remarkable and easier to make an assumption about. Not that tags should be about assumptions.

The tag is also important because for some people it is an important feature. I personally find a complete lack of nipples on a chest or breasts to be mildly disturbing. Not quite blacklist level, but I have considered it. Some people find a lack of genitals disturbing, and aren't nearly as reluctant to blacklist things as I am. But removing the tag breaks people's ability to avoid it or blacklist it, which is a pointless headache. Also, by your logic: armless, eyeless, legless, headless, faceless, faceless_male, and every other noticeable lack of something you normally expect to be automatically included would have to go as well. Even topless and bottomless would have to be axed, because why tag a lack of clothes? shouldn't you only tag if clothing is present?

But I think that these are all are useful tags when something isn't there that should be. Or when the lack of it is useful, like bottomless and topless are useful for searching.

Bottom line: when something is reasonably expected to be automatically included, and it's missing, then it should have a tag. Most pictures don't need it, but these tags exist for exceptions that do need it. I don't think it's a good idea to collapse them when they serve a purpose.

This line of logic also assumes that all tagging is complete, so that just searching -nipples would replace the need for a no_nipples tag. In reality -nipples will get mostly pictures where nipples weren't tagged but are visible (incomplete tagging), or there was no place for a nipple to even be expected to show up. So therefore, no_nipples serves an actual purpose different than -nipples. Getting rid of these tags is just ill-thought through.