Maybe start from the assumption that the people designing election systems have considered someone printing extra ballots? The system I'm familiar with has safeguards to ensure that the only ballots that get counted come from eligible voters.

Unfortunately this is a false assumption to make. Yes, they may have considered it but ultimately there is increasingly very little that can be done to impede such fraud. Frank Abagnale explains how paper-based fraud is easier than it ever has been due to technological proliferation[1]

[1]https://youtu.be/x0fEA0MsiV8?t=2266

The authentic ballots are not just authenticated against themselves, they are kept secure.

You need a conspiracy at every precinct where you replace or introduce ballots.

I realize it isn't a perfect system, but you can't just fire up your laser printer and leave the extra ballots sitting outside the polling place.

>You need a conspiracy at every precinct where you replace or introduce ballots.

Indeed. I'm not sure if you watched some of the clip I linked to but that it one of the things Abagnale speaks to. With decreasing budgets, increasing corruption, or a simple lack of ethics it is easy enough to compromise an individual and thus the whole system which they administer. Any social engineer will tell you it is far easier to hack a person than to hack a system.

This is why I would argue that a more automated electric system, one which relies on less human administrators, would would be more difficult for the average person to compromise than a paper-based system which relies on a higher number of human administrators.