Why thumb up on video that I disagree

On youtube, sometimes I click thumb up (like) on video that have footage I disagree with.
For example this one
http://www.youtube.com/watch?v=vGC9XtnHSU0

The reason why I clicked thumb up is that I see they put it up to show us the truth. Showcase the brutal activities some people choose to do.

It's a like & dislike situation. To me, it's rather silly to dislike if you agree such cruelty shouldn't have happened. This only makes sense I clicked like when I disagree.

This is just a spot of a "freaking huge iceberg", I'm just wanting to clear this out once and for all.