That would not generally rise to the level of lethal force. People also kill flies, roaches, etc. and the self defense justification is a lot more flimsy there

That would not generally rise to the level of lethal force. People also kill flies, roaches, etc. and the self defense justification is a lot more flimsy there, particularly when people will preemptively attempt to wipe them out, based on the assumption that they will do bad things... because of their species. Interestingly, that also points to one sort of intelligence. That is to say, you can't assume anything about how a person will behave simply because of what race they are. You can reasonably do so with unintelligent animals (e.g. you can assume a mosquito will bite you, given a chance).