Perhaps the reason why it is best to date Colonel Kira is because it would keep her from ever doing this again with Constable Odo.
I think I speak for all of us when I say, "Eewwwwie eewwwwie eeeewww ewwww!"
Sure it might be fun to date a shapeshifter for a little while, what with him coming into the bedroom late at night a foot shorter but with a schlong the size of a watermelon, but after a while I'm sure that a demanding woman like Kira expects something more from a man.
Like eyelids.