Your math is not correct on this. You have stated the rate of deaths per mile, not the probability of not dying per mile, e.g. if 2 people died per mile, then the probability of dying per mile is not 200%.
I believe this should follow a Poisson distribution, i.e.f(k;m) = ((rm)^k * e^-(rm)) / k!, where k is the number of deaths, m is the miles traveled, and r is the deaths per mile. Then, the probability of dying after traveling m miles is 1 - f(0;m), i.e. the probability of no deaths occurring. Thus, the probability of dying when traveling 10^6 miles is 1 - e^-(7.3 / 10^9 * 10^6) = 0.727%.
This is like saying it is okay to kill a lonely person with no friends and family, as long as it is an instant death.
I don’t agree with you that suffering is the single center concept to base your moral judgement on these issues. Not all living things that i care about are able to suffer, and I do not care about all living things that do suffer. I do not care that i cause a mosquito suffering by killing it (wounding it), if it is sucking my blood, or even just being annoying when flying around me, because I value my comfort above its existence (and suffering). I expect you do the same? This is speciesism.
Except we both agree that racism is wrong. We do not both agree that speciesism is wrong.