The idea is, we've not had robots to do our
killing for us in the past.
A bit of trivia I picked up in a robotics class: Most of the common definitions of 'robot' include cruise missiles, which we've had since the 1970s at least.There is an interesting difference, though it's not the one you've chosen to frame your comments around. It doesn't matter that the Roomba has no more moral agency than a sack of hammers. That's a point the author passes by on the way to the real crux of the article, which is that autonomous machines have a way of masking this fact in a way that tricks humans into ceding their own moral agency. That example of a person who wouldn't knowingly vacuum over a cricket but happily uses a Roomba is just a less politically-charged proxy for the question of autonomous military robots carrying weapons.
Or another way to look at it, is enough technological progress and specialization results inherently in a fragmentation of what morality means because the concept can't fit the same way in everyone's head (square peg round hole). Its a natural result that some fraction of the population will just meaninglessly babble while other fractions laugh. Its possible to interpret this has already begin with respect to evolution, geology/age of earth, climate change, stem cell research, euthanasia, gay marriage, etc...