No one is. A lot of people who are preferring a plant based diet due to moral reasons are well aware of such "roadkill".

Thing is, we're not breeding them into existence. These deaths are accidental and if there were a technical solution to the problem everyone would be in favour of that. In the animal industry on the other hand everything is intentional. Both, the scale and the moral intentions are a completely different world there.

So, from the moral stand point of veganism: is it bad to kill animals? Yes. Is it worse to kill animals intentionally on an industrial scale, which could be prevented, than accidentally on a much smaller scale during plant farming where it currently can not be prevented? Absolutely, yes.