I mean, there are plenty of instances if you are willing to look... https://en.wikipedia.org/wiki/List_of_cases_of_electoral_fra...
Hackers rather trivially were able to hack optical scan machines back in the 90s or early 2000s. Defcon famously has its voting village, where hackers hack voting machines via numerous means. If you think this isn't happening (or at least being attempted) in reality (by either party, and/or outside countries) you are naive.
> That's not how rights work. Would you say that there should be a "barrier to entry" for freedom of speech or gun rights?
Yes, there is a barrier of entry for freedom of speech and gun rights; it's called holding on to freedom itself, and it is a VERY difficult and bloody ordeal that can be lost extremely quickly if not protected. (See all non-free countries, or even parts of Europe where you can now be jailed for making certain comments online.)
I never said the barrier for entry should be a test, like the "literacy tests" we implemented during Jim Crow, but if you aren't willing to give up something for your freedom, you probably don't deserve it. (Not saying you must necessarily give something up, just that you must be willing to give something up.)