The first dose at 600 mg/m2 is basically to establish dose safety for all patients. If there is poor white blood cell count recovery after 4weeks at that dosage, I suspect the oncologists, who are very well versed in dose modification and dose delay in that situation, would act swiftly accordingly. If it is well tolerated, they would move on with the scheduled dose. This is the right thing to do when studying a drug in a new patient population.
As for justifying its use, my opinion is that we are sick patients and many of us looking for treatments. some treatments are higher risk than others. Sometimes, these risks are worth the try considering the quality of life of affected people. For some patients, the risk will never be acceptable and patients should not be forced into something they do not want.
It just adds options, is how I view it.
And yet, because there are few options (and no approved drugs by FDA) patients should be given compassionate access to drugs.