Earlier quoted context omitted.
You give one citizen one vote on the chain. They can personally verify that their vote was counted because the chain is visible. Counts can't be rigged because the entire chain is public. Voters can only vote by going to a physical location where they use a multi-key signature, one by the voter, and one by the local polling station, avoiding people selling off their keys. This is anonymous, traceable, and the vote ca…
As I see, the problem is not that the vote can be altered, but that the vote can be bought and the fact that person voted in the right fashion could be verified by 3-rd party much more easily (screenshots/whatever). The privacy of voting booth could give at least some chance to change mind/lie to the third party.
In fact, with a blockchain-based system, the vote could be held in "limbo" until the voter decides to cast it, or you could give the option of creating fake screenshots to deter anyone "buying votes". You can't do this with a paper ballot.
The real problem is compiler and hardware level.