There might be a way of storing it on chain by encrypting it first with your public key. This way it would work in every client you used.
I'm not sure it *should* be secret. Likes aren't, why should the fact that you dislike be secret? If I block/mute someone, I don't care if they know.
In fact, you could decide that if 1 or more of those you follow blocks someone, they're blocked for you too. If downvoting happens, it could work same way. Not censored, but filtered.
I've been thinking of that too. Knowing what users are the most muted ones might be a very useful information.
