According to the link you gave the David Brin quote should read:

“Pain, exploitation and death were the attractor states for a billion years. Mr. Larimer and other cyber transcendentalists bear a burden of proof that This Time It Will Be Different..”

I wonder if Brin edited his article after you quoted it.

Anyway, the “burden of proof” only applies to science and jurisprudence, not to economics, politics, philosophy, speculations on social reform, etc.. Humanity goes to war over hypothesis, opinion, and speculation. Very few ever set about proving anything.