The OP did not hint at any of that. You should have explicitly stated "sites like /jp/" if you did not want to have people assume to which communities you were referring.
As far as /jp/ is concerned, it suffers the problem that 4chan suffers in general: if a comment is tangentally related to the topic at hand and it not too obnoxious, it will rarely warrant a deletion. Also, /jp/ is hardly a small board compared to the average of all imageboards, so it should hardly surprise one that many who are not NEET, and who do not have a mentality of anonymity that once graced even imageboards like 4chan, still find interest in Otaku Culture to the extent that they will actively browse and attempt to contribute content to the site, often to your distaste.
The Overton Window is a reality in the hard-to-enforce online communities, and the primary positive result has been the specialization of online communities, such as the splintering of /a/ and /jp/ into communities like Tohno-Chan, or of /r9k/ into WizardChan. The incoming group gets their unmolested access to the previous board, and the previous group gets unmolested access to the neo-community, assuming the chnge in community alienates a significant number of veterans.
If it irritates you so much, do your part and contribute to Tohno-chan, so that you will not have a need in the future to browse /jp/.