Users need to be identified, its not a matter of if in the case of electoral voting.
Information can be stored on the blockchain without it being publicly available for everyone or anyone to see.
In such cases a user can store some type of sensitive information encrypt it and shard it on the blockchain, its there but the hidden information is not viewable to anyone who doesn't have access.
Then we have homomorphic encryption which could do operations without anyone having to see the hidden data.
Conclusion
Not everything on the blockchain is open for everyone to see, you can hide information in plain sight.