Dear Sirfoobar,
How would you know which spaces where inserted with the TAB key and which with the space bar. The whole idea behind spaces rather than TABs is to make the file look the same on different boxes, with different text editors having different settings.
And why can’t you select the line/lines and type SHFT-TAB. That un-indents all lines selected to the tab stops even if the number of spaces is not an integer multiple of the tab spaces.