> It would be better if voting would cost money

Voting does indirectly cost money. The rewards pool used for voting content comes from increasing the supply of Steem, which puts pressure on lowering the price of Steem (inflation). To cover the cost of inflation requires self-voting. Every vote for someone else is distributing coins to someone else which is like paying. The purpose of voting is to reward content that adds value to the platform. This is a community effort.