So which is why some form of punishment is needed when it comes to voting cartels. I think Vitalik's Capser DPoS makes sense. You can incentivise token holders to hold more token by making them participate in the blockchain, but if you find that they are part of a double spending attach (for eg), then you burn their house down (or take away all their tokens..)
if you don't punish the wrongdoers, they won't have a reason to stop.