You're losing your mind at the idea of ANY land transferring from federal to private hands. You very much are simping for the feds, lol. People buy barren lots all the time and develop them. It gets ridiculous when there is a checkerboard piece of federal land adjacent to developing land. So many scream at the idea of the feds losing it, but no one ever recreates there.
This is going to come down to personal politics, but the answer to your question is that Mike Lee and the GOP are better than the alternative on almost every other issue. I could understand wanting to vote Lee out in a primary, but to act like this one issue negates all of his other work is plain foolish.
You do not have any demonstrable evidence or reliably accurate forecast for Lee's or anyone else's plans or eventual outcomes involving a possible sale of federal lands. You have a bunch of extreme-scenario speculations and scare tactics from the public lands lobby, which is a career for some and involves a ton of players with other agendas beyond public lands. Ryan Busse is a prime example.
I touched on this in another comment, but yes, you are right, there are plenty of specifics to argue against, but screaming that absolutely no public lands should ever be sold and that every politician with an unfavorable position on this one issue absolutely needs to be replaced by the alternative, it's a foolish and unrealistic rant. It flies in an echo chamber like RS, but it's not a sensible conversation. Most people in this country don't hunt or use undeveloped public lands.