What's to stop a maniac with a wrench "convincing" you to transfer all of your money to his bank account electronically?

Money transfers can be rolled back rather easily and unless that maniac has an offshore account, wants to be on the run for quite some time and get close enough to someone with enough money to actually make it worthwhile, it's hardly going to work out or be worth the trouble.

Being coerced into voting for a certain party is a whole different problem, with different actors. You're not going to run the election again when the spouse of someone pressured them into voting against their will. How would you even want to prove it had happened in the first place? There's not going to be a paper trail without giving up voter secrecy, which is yet another problem.

And how would a paper system prevent that?

At least where I am from you must go and cast a vote privately alone on paper. So this can't be executed on big scale, you could only force couple people to cast a specific vote without getting kicked out or arrested.