This is something I'm curious about. For posts that emphasize the crotch in however small a degree, like having the legs widely spread or the character being in a sexy pose, I can understand the tag being applied there.
But something like this getting the tag is odd: https://e621.net/posts/4674928?q=featureless_crotch
It's exactly how Rigby is depicted in the actual show he comes from. I know the child post is explicit, but in terms of just the initial image there's nothing sexual about it.
Or something like Pikachu. Like, here's a screencap of him from the show. Despite being completely innocent this would get the tag too, right, if the image above got it? https://facts.net/wp-content/uploads/2023/07/20-facts-about-pikachu-1689578613.jpg
Here's a few other ones that feel like the tag is unwarranted:
https://e621.net/posts/4664678?q=featureless_crotch
https://e621.net/posts/4682856?q=featureless_crotch
https://e621.net/posts/4682727?q=featureless_crotch
https://e621.net/posts/4660037?q=featureless_crotch
https://e621.net/posts/4662705?q=featureless_crotch
https://e621.net/posts/4660026?q=featureless_crotch
https://e621.net/posts/4657500?q=featureless_crotch
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And just to be clear, this isn't a blacklist issue. I have no issues with images being explicit. I just find it odd to attach a tag emphasizing the lack of genitals in images where nothing remotely sexual is occurring.