Adding the ability to express your opinion on-chain in a well-defined way doesn't cause any harm, and allows us to get a clearer view of what the community wants than the current best system we have - that of shouting at each other in forum posts.
It is not at all clear that this doesn't, or couldn't, cause any harm. It allows a conclusion to be promoted as "fair" when it may be nothing of the sort. You even used the phrase "provably fair" in your post. I recognize that is a being used as a term of art, but not everyone will recognize that. There is such a thing as sham votes that serve to falsely legitimize something that would seen as illegitimate if openly imposed a single party or a small oligopoly. Yet with on-chain voting, that can easily happen non-transparently.
With on-chain voting, it is impossible to know that one party or a small group doesn't control >50% of the votes, making
everyone else's "vote" absolutely irrelevant if decisions are made by a "majority". Even control of a relatively large portion that isn't itself an absolute majority, say 30% (or likewise for decisions made by a super-majority threshold) by one person or a group acting together gives very disproportionate influence. (BTW, I'm not referring in any way to Just-Dice here, I'm referring more generally to beneficial coin ownership, on the assumption that you pass through voting rights as you have promised, or that people withdraw from JD in order to vote.)
It is taking what is already a system that is vulnerable to disproportionate influence by large stake holders (proof-of-stake) and further concentrating that influence with the very same large stake holders. One
might imagine that stake-voting in a proof-of-work chain could make sense because the concentrated influence of large stake-holders could counterbalance the concentrated influence of large miners. But here it makes no sense at all.
On-chain "voting" is done for soft-forks only when they are non-contentious, and the threshold is extremely high (typically 95%). It is more a measure of how many have upgraded to the latest version to avoid breaking things than a decision-making process.
BTW, as bad as shouting at each other on forum posts might be, one person really can't shout 10 000 times louder than someone else, especially if obvious sock puppets are ignored. That's a feature.