I would suggest as follows:
How would the right/left thing work with the Polygon or Rotated Rectangle selection methods?
The key thing is having user choice.
- - the choice of direction based selection for the standard rectangular selection
- the additional choice of direction based selection for all geometry methods
I think the ideal would be to
(1) add a third selection method, "All in", "Some in", and "direction sensitive".
(2) add a long-requested keyboard shortcut to toggle between the 3 options at will.