Well well, I remember this 'discussion' last year =P I'll copy-paste my points from then here. Granted I'm not that active anymore so it will bother me less. Also not a mod anymore, so ignore those parts.
Regardless of the occasion, posting unrelated spam on an image board dedicated to hypnosis/mind control should be deleted.
- It goes against the site's posting rules. This is a hypnosis/mind control board. You post images related to hypnosis/mind control. If it's not, it gets deleted.
- "Regardless of occasion". What makes April Fools special in that everyone gets to post spam for today? Why not do that for Christmas, Valentine's, New Years, etc?
- Related to above point, please note what is not allowed is spam. On Christmas people do not post Rick Roll all over the place. Artists draw Christmas hats on hypnotized OCs. You're free to make jokes and have fun by posting comics related to the hub.
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Now, regarding your/others points.
"It's only one day" - I could say that it has no relevance. It's actually addressed in my above points as to why we should bend the rules for April Fools only. I could say that it's a slippery slope of '1 day is okay, what about 2? 3? a week?' I could say that this statement could easily be reversed to tell you to leave the site for one day and take your business elsewhere. There are plenty of other places online that embrace April Fools, why not enjoy yourself there instead of causing a commotion here? Honestly I was just going to not look at the hub for today and try to ignore it all. Then I remembered I should probably still mod the forums (loosely), and saw Dreamshade's post and decided to help.
"Just use the blacklist" - If this excuse got through, we would not need to delete anything at all. Why not just go on Gelbooru and search mind_control, and act as if you've blacklisted everything you didn't want to see? The DNP list? Nah, the artists can just blacklist their own works. Other people enjoy their work, what a killjoy. The purpose of a blacklist is to help people hide images they don't want to see (or are illegal in their country), but still related to the hub
"Helps the community bond" - Judging by the mixed reactions in this very post, I would say it would help a portion of the community bond while distancing another portion of the community. This happens in pretty much everything, but the problem is that the portion that is being driven away is driven away because this hypnosis and mind control board is not actually posting hypnosis and mind control images.
"No fun" - If you could convince me that it's okay that would actually be good because then I would actually be able to enjoy this day in the future >_> But for now, no; you're having fun at the expense of the purpose of the site, at the expense of others, and you're demanding that the rules be bent for one day just so you can have your fun here instead of on other sites that embrace the holiday.
In case anyone's interested the whole 'discussion' last year can be found here.
hypnohub.net/post/show/46885