You need to distinguish between two very different things. In vote result manipulation, a single actor can modify votes wholesale. In voter fraud, an individual who shouldn't vote does, or pretends to be other people and votes multiple times.

The risk of the former is huge and hard to detect. The latter, despite claims the contrary from certain news outlets and Presidents, is actually extraordinarily rare.

Voter ID cards are claimed to address the second issue, even though they actually alienate far more legitimate voter than fraudulent votes.