You trust paper voting because voting booths are operated by representatives of the different candidates. When it comes time to count no one will let their opponent steal votes for themselves. And the reason you can't add your digital signature to your vote is that you could then prove to someone you had voted for candidate X and collect your bribe.

People that want to propose complex electronic voting systems need to first understand the requirements of an election and how the paper voting achieves them. There's quite a lot of well thought-out systems thinking in paper voting that people just don't know about.