As far as I can tell, in all other areas of Rhino, a selection box dragged from left to right selects only what's within the box, dragged from right to left selects all within and crossing box lines. Combined with Shift key, objects are added to selection. Combined with Ctrl key, objects are subtracted from selection.
Within the Sweep command, Ctrl-select is toggling the selections. Toggling is much more difficult to use when trying isolate a curve of interest.
Rhino's established selection conventions work really well. Can we get them back on this command?