It’s a large and incorrect assumption, and not mathing, to lump non-voters into supporters, especially when the administration is purging eligible voters.

Rhetorically: why is it "implicitly approve" instead of "implicitly disapprove?"

The only thing you know about them is that they did not vote. Even using your assumption of their beliefs ("both sides are the same"), that position is generally affiliated with disapproval, not approval.

I'm in one of the many states where my vote doesn't matter. Deep red. Doesn't make me a supporter

This is extremely lazy and unrigorous reasoning that could be extended dishonestly to any number of things. Oh, you aren't protesting genocides? You must support them then. Oh, you're not helping feed hungry people in poor countries? Guess you support child starvation. Oh, you're not contributing to the Rust ecosystem? ...............