Because if you don't have that, you literally don't have a country.

Why not? By definition, you almost can't ever have perfection in elections. Our elections are already fair and secure, without making any further changes. You might not know how many people turn up and engage in in-person voter impersonation fraud, but it cannot be very high - because there are so many procedures in place that allow for such things to be caught both during and after the fact (and people check nearly every vote every time there's a tight election) it couldn't possibly go undetected at any material amount.

The flip side is there as well - one could argue that if our elections aren't open to participation in by all the people who are supposed to participate in them, then we will literally not have a country. If you start carving out millions of folks that are citizens and allowed to vote and keep them from voting, you're making the elections less fair and secure also.

So unless you have an actual reason for imposing a burden on people that would result in people who are lawfully permitted to vote being unable to vote, you shouldn't do it. And there isn't an actual reason, here. If this were going on to any material degree, people would get caught. They'd show up pretending to be someone known to the polling volunteer, or a bystander checking in at the same time. Or the person they're pretending to be would show up later to try to vote - or even sometimes when the person was still there. Or if you do a survey of a few thousand voters after-the-fact, you'd find several who would tell you that they didn't actually vote on election day. That's why we keep all those records, and why the political parties have access to all those lists.

Literally tens of millions of ballots get cast on election day, so 0.1% of those would constitute hundreds of thousands of in-person votes - cycle after cycle after cycle. There's no possible way that you wouldn't be able to detect large numbers of in-person fraudulent voting over time if it were happening at a level that "you literally don't have a country."