Oh, I fully agree—like I said, legally they're not at fault, because you'd more or less have to be tailgating and/or inattentive to crash into them just for braking unexpectedly.

But if there's an existing system and culture of driving that has certain expectations built up over a century+ of collective behavior, and then you drop into that culture a new element that systematically brakes more suddenly and unexpectedly, regardless of whether the human drivers were doing the right thing beforehand, it is both reasonable and accurate to say that the introduction of the self-driving cars contributed significantly to the increase in crashes.

If they become ubiquitous, and retain this pattern, then over time, drivers will learn it. But it will take years—probably decades—and cause increased crashes due to this pattern during that time (assuming, again, that the pattern itself remains).