There are a lot of arguments about social pressuring users into voting a certain way. But not having votes public also leads to a lot of vote manipulation. Especially from the Hasbro's.
Lemmy is a lot like the early days of the internet right now. Very easy to abuse and mostly running on users not doing so. Bot accounts will start being a bigger and bigger issue with the growth and Lemmy so there needs to be a way to combat this.
Votes are also already not private as many users said. Just by running an instance one can see all the votes.