Same but different issues. Now you have to know that the dots were filled in correctly to be readable. Having someone make an obvious attempt at selection but not readable by the reader is also problematic. No reason to not count their vote. You may laugh about not being able to do it correctly, but it happens.
Only if the scantron shows that each position on the ballot was counted and the voter is not allowed to leave until the person monitoring the scan confirms with the voter their ballot was scanned would this give confidence. Any issues with the scan, and the voter is allowed to correct the issue. There should never be an issue of reading the ballot by the scanner as an acceptable outcome.
of course, all of this is assuming in person voting only
Checking each ballot for completeness sounds like a good improvement to the system. Right now people are just expected to mark carefully and double-check their work before feeding their ballot into the machine and request a new ballot if they mess up.
It might slow things down a little bit, but making sure that the machine can detect a vote for each race/question (even if it's just "Abstain") would make sure people didn't forget to fill out something and help prevent the fill-in-the-bubble equivalent of hanging chads.
I like the idea that "abstain" should be an option for each position on the ballot to remove the ambiguity of it just being skipped mistakenly. Require every position on the ballot to need a response from the voter regardless. That would definitely simplify the tally process even if it does require the voter to go back to fill in additional spots. Better to be right on even if it takes 30 more seconds.
Only if the scantron shows that each position on the ballot was counted and the voter is not allowed to leave until the person monitoring the scan confirms with the voter their ballot was scanned would this give confidence. Any issues with the scan, and the voter is allowed to correct the issue. There should never be an issue of reading the ballot by the scanner as an acceptable outcome.
of course, all of this is assuming in person voting only