The first article isnät really any help. It throws out impressive numbers on all sorts of things breastfeedign decreases. But it only talks about breastfeedign lowering the risk of x by 35%. That doens't really mean anythign if you dont know what the orginal risk was. Even 70% increase or decrease can be marginal if the orginal risk was tiny. 

Example (completly made up numbers):

Chance that formula fed child gets leukemia is 14 in 100 000 or  0,00014% 

Now if breasfed child has 30% lower risk of getting leukemia the new risk is : 0,00014x(1-0,3)=0,000098% 

Both chances are immensly small. And I wouldn't  consider it bad parenting to take the slightly higher but still very marginal risks.

The other article seemed more promising, but since its just an abstract its really hard to make sense of the results.