I try to make a point of flagging any of my NSFW content as "sensitive content". If you are using a NIP-36 compatible client, it should filter it out for you. If not, you always have the option of muting me.
The whole point of a censorship resistant platform is that you can't keep anyone from posting anything. That includes using hashtags you wish they wouldn't. The responsibility is on you to take measures to filter out what you don't want to see, because even though I very rarely post to #plebchain, there will be plenty of accounts that will in order to get engagement so long as it is among the most popular hashtags on here.