I know you weren't replying to me, but it seems people here (and elsewhere) are using "mail in voting" to mean different things. To some it just means the option to deliver your ballot via the mail. As you said, this has been going on for many years. To others "mail in voting" also includes the state mailing ballots to ALL registered voters, not just those that request it. I believe some states have been doing this for several years, and some may have started doing it this year due to COVID. (I don't know this for sure, and I don't feel like looking it up.)
I personally have no problem with making it easy to vote. I do think there are potential issues when you start offering the various initiatives. Mailing ballots to everyone, extending ballot acceptance dates, allowing ballot harvesting, and loose/no ID requirements all add some risk of fraud. If a state chooses to allow any or all of these initiatives, they just need to put processes in place to reduce the risk as much as possible.