I think Oregon, and maybe Washington too, have had mail-in voting for a while. Nevada's trying to set it up before November - good luck. Don't know about Utah.
But you've got to admit there's more room for mistakes to haven, if nothing else, given the track record of the USPS in delivering mail. A large portion of my mail is delivered to someone else. If I mail a letter to my neighbor, it goes to Birmingham, then hopefull comes back 3 days later. If you order a package, there's a good chance it'll never make it, at least in one piece. So overwhelming them with 150 million people receiving and mailing back ballots has the potential to be a nightmare.
And none of that includes outright fraud. There has to be a greater chance of fraud than going to your poll, showing a photo ID while being checked to see if you're on that precinct's roll, filling out your ballot, and running it through the machine. Here, and presumably other places, they even run your DL or other voter ID through a scanner to make sure you don't somehow vote twice.
I don't really see anything "conservative" about insuring only qualified voters vote, and vote just once. Everybody should want that. Now if you want to argue the legitimacy of the electoral college, then I might be on the side I'll presume you're on (a vote should count the same regardless of where you are).
One more thing (or two or three) - if you don't drive, there are measures in place to get you a alternate photo voter ID. If you can't get to the poll, someone will easily take you. It doesn't matter what color you are or what party you favor.