I live in Utah where I've only ever voted by mail, and we're a very red state. I've never had anyone express concern about our mail in voting process, the main concerns are typically over voting machines (which I share, I don't trust single points of failure with minimal audit capabilities). Mail voting is equitable since you can either drop off a ballot or mail it, they can be tracked to ensure they're received, and they can be recounted in person.

So the opposition to mail voting seems centralized in areas where Republicans have less control. So it's obviously BS. How they're not suffering for this from independent voters is beyond me.