There are more than one way to say that, depending on what you think with "propósito".
Anyway, with some guesswork here goes my 2c.:
(1)"There´s no point getting angry."
(2)"Getting angry is a waste of time (and energy)."
(3)There´s no point getting mad at him/at that.
(4)'You have no reason to get mad at him" or "I don´t think you have a valid reason to get mad at him/her."
(5) "I think you are getting mad at your boyfriend/girlfriend for no reason."
(6) "I think you are getting mad at your boyfriend/girlfriend for no good reason."
1-3 In the same sense, and 4-5 is in slightly another sense.