I wouldn't, and I like trains more than most people do. I'n sticking with my own car for transportation for the foreseeable future, and everyone else who owns a car is doing the same. I'm not going to put myself in a large metal box full of other people who might be sick.
Now maybe a train stuffed with non-mask wearing people talking constantly would be a different issue.
Why, yes. I remember taking the high-speed train from Madrid to Barcelona some years ago in the preferente+ class, which cost me about 90€, and there was so much room that, with the exception of my side chair, I couldn't touch anyone else if I reached out in any direction.
And IIRC each carriage had about a 50-seat capacity.
That's a far cry from your typical sardine can experience in any airline, including in high-end seats.
Tell me if I read it wrong, but you meant to say that €90 is a small amount right?
Building more rail lines ... well that's another matter.
Trains (the long-distance sort, at least) tend to be a lot less crammed than airplanes, and you can open the windows.
The engineering considerations of air exchange with the outside environment are admittedly far simpler than jetliners.