I have had a problem with steel cracking and breaking. On two different bikes. One of them broke at the steer tube, broke at the chainstay bridge on both sides (that's how I found out about the difficultly of welding the tubes, and, finally, broke at the drop out. Steel isn't invulnerable.

I've also had a cracked an aluminum frame. No drama or the frame turning to dust under the rider or exploding...it just cracked at the bottom bracket bridge like the steel bike.

However, you are missing the point. Steel, nor aluminum, are that difficult to weld. But they do require a different skill set than your normal backyard mechanic or even experienced auto mechanic with good welding skills may possess. To say that you are going to buy a steel frame because it can be easily repaired in outer Polucaville is setting yourself up for disappointment.