Several years ago, when asked whether she would participate in an event that centered around the Vietnam War, Mother Teresa responded by saying, she would not be interested in marching against the war. However, she added, if you were to have an event marching for peace my attendance would be guaranteed. She understood the principle of 'for vs against', and mentally, how it effected the issues of the day.
You see, I believe that what your for strengthens your mental position, while what your against only serves to weaken that same position. Simply put, you may be against gaining weight or you may be for living a healthy lifestyle. Certainly the later forces a stronger mental position that, when acted upon, produces a more favorable outcome.
You can be for or against, the choice is always up to you!