Help me understand why anyone would be opposed to proving citizenship in order to vote

I don't follow politics terribly closely because for the most part it just makes me unnecessarily angry whenever I do read up on it too much. Recently however, I saw a story about a bill that narrowly, and of course almost entirely along party lines, passed in the House of Representatives where the bill in question was reportedly all about proving citizenship in order to register to vote and also to vote.

As always, I am posting this as a genuine question, not as a lecture to anyone else out there. I try to understand the left's opposition to things but because of how biased our media is I feel as thought it is nigh on impossible to get any real information about basically anything that is happening.

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It's called the SAVE Act and the vote went 220-208 and unless I am reading bad information in my simple search, there are 220 Republicans and 213 Democrats in the House.

So this means that not a single Democrat voted for this bill and I would like to know if anyone out there can tell me why. I mean, I understand that in today's political turmoil that virtually anything that goes on in the House, or the Senate for that matter, ends up going down party lines, but unless there is a bunch of shit in the bill that doesn't actually have anything to do with non citizens voting (which I presume there is because there almost always is), I can't understand how anyone would really be opposed to non-citizens voting in US elections.

I was able to find a few quotes, but to me this sounds like someone is making this out to be a much bigger deal than it actually is

“Coupled with President Trump’s recent anti-voter election executive order, the SAVE Act would end the voter registration process for all Americans as they know it."

and

Republicans have repeatedly failed to present any evidence that noncitizen voting at a federal level has ever affected the outcome of any election

Ok, that very well may be true, but at the same time wouldn't it be a good idea to ensure that non-citizens can't vote in US elections, even if it is a small amount of people? I'm a simpleton redneck with a rather high level of specialized education, but that doesn't mean that I am trying to act like I know more than other people about all things. I have no high horse. I'm just trying to understand why all Democrats would be opposed to this.

When Republican governor Youngkin did such a purge to the Virginia voter rolls, 1600 people were removed because of non-citizen status. I'm not suggesting that I know that all of those were actually non-citizens, nor am I suggesting that this is a significant amount of voters. According to a quick search there are over 6 million registered voters in Virginia, so yeah, this is a very small amount.

At the same time though, just because something rarely happens doesn't mean that it shouldn't be addressed does it?

So to the sensible and better-informed-than-I-am people out there, please help me understand why anyone would be opposed to this bill passing. To me it just seems like people are not going to vote for anything that the other side comes up with, no matter what it is about.... but then again, I could be missing some very crucial aspects of why they are opposed to it because of media suppression of information and because all politicians make sound bytes that appear to simply be geared towards benefiting themselves, rather than actually inform anyone about anything.

Help me out please!