Duplicating a line shouldn't take selection into account, but whole lines

It's very useful to select a bunch of lines by dragging the mouse cursor in the middle of those lines and then duplicating those. But line duplication currently only duplicates selection, it's tedious.It should work taking whole lines into account like Delete Line function (Ctrl+Shift+K) does.Also, after doing Duplicate Line command, newly duplicated lines should be placed on new line below last selected line, and not in the same last line of the selection. It's tedious.