[hurrdurr56]

>They never stop to think that, if their moral code calls for killing all these people, maybe they should be questioning their moral code.

They certainly do think about it. The logic is invariably:

1. These are people who are holding back progress towards a future in which (according to my ideology) everybody is happy / equal / free / (insert vaguely defined ideal state here)

2. Therefore they must not want people to be happy / equal / free / (insert vaguely defined ideal state here)

3. Only an evil person would not want people to be happy / equal / free / (insert vaguely defined ideal state here)

4. Therefore they are evil

5. Therefore I am morally obligated to annihilate them

6. I am a Good Person because I am so devoted to ensuring that everybody becomes happy / equal / free / (insert vaguely defined ideal state here)