You can either "take a stance" or "make a stand" against either terrorism or racism. It depends on what you mean.
If you "take a stance," you make your opinion known.
If you "make a stand," your role tends to be active and assertive. The idiom comes from the military, where it refers to holding ground (that is, not retreating) in the face of the enemy. You don't have to literally face an enemy with a weapon in your hand in order to make a stand, but the idiom means more than just stating that your opinion.
If I told people I was against racism, I'd be "taking a stance" against racism. If I did something more active, such as stepping in and defending someone who was being subjected to racism, I'd be "making a stand."
There are gray areas in which it might be difficult to determine which idiom qualifies, but as I explained, "making a stand" is much stronger, and implies a greater degree of risk, than does "taking a stance."
Does that help?