I feel that the onus should be on the private tree folks, not on me. I shouldn't have to spend hours begging to look at their hidden trees for something I have paid for. And may not need to even see.
I think a surname search feature for ALL DNA tested trees, public and private, would be a good compromise. Then a nice email to all the private tree folks explaining that sharing creates good positive genealogy karma which we all need to break down these darn brick walls.