So much here. My only concern would be the the moisture issue, which would be obvious. I just don't see the problem comparted to other food packaging, in fact DME gets boiled so there is no problem.
Do you ever buy things from a grocery store deli? What about all the things in a store that they buy in bulk and sell as their store brand in plastic containers, many of them ready to eat salads and such. Have you ever eaten in a restaurant? Bought self serve bulk nuts, grains, flour etc. in a store? Do you eat vegetables?
Apart from the hundreds of examples of more problematic packaging than this I could go on with, I think you have misplaced confidence in the larger corporations. The U.S. has less and less food safety enforcement. I would have much more confidence that my LHBS would safely package DME than General Mills would scrupulously make sure there are less than X amount of mouse turds in your corn flakes.