It might be helpful to explain the "Lemmings behavior" for people who don't remember or never played Lemmings. In that game, during molding (actually called "building", but let's substitute Clones terminology here), you don't fall while laying down mold "steps" and stepping up onto them, even if the ground the molder is currently standing on is removed by some other action. What you can't do of course is to simply start molding while in the middle of falling;
that doesn't work even in Lemmings.
Simply put, molders in Lemmings are immune to falling, but you must still be on land (for the most part...) to start molding in the first place.
I think the current issue rt is trying to address is the case where, under normal Clones behavior, the molder
would fall and stop molding, if the ground he is currently standing on is removed. So someone sabotaging a mold bridge would not merely force a repair on the bridge, but could potentially also stop the molding altogether. rt's "selective molding" proposal would basically be a version of the above description of Lemmings behavior. I don't know whether rt's "god clone/super mold" option implies the ability to build even while in the middle of falling;
that might indeed be too powerful and weird.