I've previously discussed how negative, violent thoughts can affect people.  Fortunately, there is a way to counter those negative thoughts. 
Negative thoughts that are not directed are weak and only have a significant effect when there are a lot of them coming from a lot of people.
Guided, conscious, directed  positive thoughts can counter them. The directed positive thoughts of one person can counter the random negative thoughts of dozens of individuals.  Maybe even hundreds if the thoughts are strong enough and you really believe them.
So a simple thing we all can do is spend a few minutes each day sending thoughts of love, peace and tolerance (or any other positive thoughts you prefer) out to the world, the people, and even to animals and plants.