I've been browsing the Feedback list because I literally have nothing better to do in the evenings and I'm odd.
Anyways, I've noticed some people are hit with negative feedback, or even bans, for 'Mass downvoting. Just use your blacklist'. (Paraphrasing, but that's the gist).

That lead me to wonder two things:
1. If we're supposed to use the blacklist instead of downvote, and if low-quality art (another reason to downvote) is usually removed; What is the downvote option for?
2. Am I accidentally breaking that rule when I downvote art I dislike that's missing tags I've blacklisted? I, of course, also add the tags so my blacklist will block the image from then on. So does that make it ok to downvote?

I should note; I over-think things. My friends like to say I 'miss the trees for the forest'. The opposite of 'miss the forest for the trees'. IE: I can't grasp the small details, but I can grasp the overall idea of something pretty well. So I may just be massively over-thinking this.

Edit: Though it now occurs to me: I'm not removing my blacklist just to downvote, which may be the difference. I'm just using the downvote to give my opinion before properly tagging so my blacklist catches said images.

You can downvote posts that you dislike.
If you dislike the whole subject matter of the post, you should blacklist the relevant tag instead.
You also shouldn't deliberately seek out posts you dislike, just to mass-downvote them.

If I meet picture with weird fetish that I don't understand, than I skip it instead of downvoting. It's not a good idea to argue about tastes. If it not allowed, than admins will take care about it and delete it.

i think the point of the rule is to stop people going through tags/artists they dislike and mass disliking everything in the tag

so long as its not obviously targeted, you should be totally fine