How can we stand silent when someone is oppressed? Regardless of it is a human, a cat, a dog, a cow or another animal?

Spreading information is helping those who are blind. It is helping people to grow in love and compassion.
I started to see because people helped me when I was blind.
I became a vegan when I was 27 years - last autumn. If someone would have helped me more before, I would have become a vegan earlier.

Can we stand silent when someone is being killed - by people who don't even realize that they are killing someone (e.g. a person drinking a glass of milk doesn't understand this causes the murder of a "milk cow", male calves?
How can we stand silent if someone is oppressed?
Would we stand silent if we saw someone getting killed on the street?
If not, then how can we stand silent when someone is getting killed by people's eating habits? How can we sit and just look?

Except for all of the suffering,pain, slavery and death that is inflicted on the animals -- which is never ethical and can never be justified by any means - ALL diary operations (and operations with other animal products) are having a huge environmental impact and is causing poverty,starvation and huge global warming, which will cause a vast amounts of droughts and floods with many more people and other animals killed:
http://comfortablyunaware.com/blog/the-world-hunger-food-choice-connection-a-summary/
See also this: http://www.youtube.com/watch?v=Fws0f9s4Bas&feature=em-uploademail