Truly destructive ideas do not spread because of open-mindedness, but because of stupidity and ignorance. People should always give ideas a chance, no matter how outlandish they may seem. The benefit of this is that in an educated society, the destructive ideas are weeded out of the discussion and the game changing good ones gain support.
Unfortunately we do not live in an educated society, and open-mindedness is a virtue that seemingly fewer people are embracing.
Someone can feel free to post statistics they find on a random website about the fact we have a high literacy rate, or graduate more people from high school or college. This does not mean they have been taught the skill of critical thinking, and often do not possess the means to sift through information and correctly choose the right answer.
While information can travel faster than it ever has in the history of the human race, and more people have access to all information, their lack of the above mentioned skill simply makes them ignorant followers who do not think an idea through to conclusion, but simply stop at the benefit to their life today.