Final answer:
The lines are spoken by Lady Macbeth, revealing her feelings of regret and the theme of ambition's psychological consequences in the play.
Step-by-step explanation:
The character in Shakespeare's Macbeth who speaks the lines "Nought's had, all's spent, Where our desire is got without content; 'Tis safer to be that which we destroy Than by destruction dwell in doubtful joy" is Lady Macbeth. This line reflects Lady Macbeth's increasing unease and regret over the murderous plots she and her husband have undertaken to achieve power. It showcases the theme of the psychological consequences of ambition and guilt that runs throughout the play.