The best argument against the EC video is when they tell when it's okay to massacre people, which is if they have the wrong politics (With the examples of Nazis and Klansmen).
It's wrong on many levels:
1. It's outright sociopathic since killing people for beliefs is insane and illegal. Especially with Klansmen, who don't always kill nigros and can be just regular racists.
2. The definition of wrong politics is subjective as hell. Even with the nazi example, you don't kill "Ze Nazis" because they are nazis, you kill them because they are fighters of an enemy country. Unless EC is arguing that the population of Germany should be genocided it makes no sense.
3. As jlongbone noted, the entire argument falls apart if you have a person indoctrinated in those politics from an early age and didn't have a choice like the evil races.
4. It also falls apart from the other side, since you never go into an ork village to kill everyone but are always attacked first, you can always say that your attackers were people with wrong politics/worldview and thus you are justified in killing them (ie, good orks exist but you don't see them).