The permanence of data on the blockchain isn't inherently a problem, it depends on how it's used. For instance, a 1BTC deposit is permanent, but a 1BTC withdrawal still means the account has, after the withdrawal, 0BTC.

So it seems here that the presence of the vote, in the ledger history, is not inherently a bad thing as long as there's a means to unvote it, AND that the unvote actually does something meaningful. That is, if it undoes demonetization, has the appropriate counter effect to reputation systems, etc.

Now, I don't know steem based platforms well enough to know if these effects are part of it, but were they to be, then immutable block chain data wouldn't be a problem.