That's just fear mongering. Absentee voting by mail has been a thing for centuries. Attempting to limit it to people who are unable to vote in person doesn't do anything to make it more secure, and is a very weak control. It's not like they're going to check up on every single person who claims to have a specific reason they can't get to the polls. Beyond that, no-excuse absentee ballots have been a thing in many states for decades. Three states have been mailing absentee ballots to every voter automatically for a decade or more. Despite this long history, there is no evidence of widespread fraud or other problems resulting from it.