Firstly, you're wrong, there is plenty of video evidence of a knife being thrown. Secondly, you're just trying to bring irrelevant issues in here... this is not the case of some guy being shot while running away. The cop involved here is not the one in London or elsewhere, and he very clearly was being aggressive here.
Let's flip things around for a second. When someone attempts to use deadly force, why should they be entitled to be treated with kid gloves? Why should the people responding to a situation take on additional risk to themselves or bystanders instead of taking the most expedient action to end the situation. If you threaten someone else's life as far as I'm concerned your life is forfeit. If they happen to take you down alive with a non-lethal shot or something else you should count yourself lucky. If your "doing something stupid" involves throwing knives at people you absolutely should expect to get shot.