This is an article defending Mims against the charge of misrepresentation. But it doesn't look as if Pianka advocated setting the ebola virus loose. His claim is, I think, that we have to control the population before viruses do it for us. So he supports something like the forced abortion one-child policy they have in China.
However, if you believe that there is no intrinsic value to human life as opposed to other life, and you think that what does have intrinsic value is biodiversity, you think that human population needs to drop a few billion people in order to insure the best chance for biodiversity, you have the power to launch the ebola virus in order to achieve this biodiversity goal, do you then have any reason not to do so? Suppose you were in a room with Pianka*, someone who has adopted Pianka's ideas and pushed them to this logical conclusion. It reminds me a little of Alfred Hitchcock's Rope, a movie in which a philosophy professor is shocked to discover that two of his students have used his nihilistic philosophical ideas as a pretext for murder.
I'm more concerned about the underlying ethical convictions behind what Pianka said than I am with the question of whether he said "Yes, we ought to go do this." Ideas have consequences, and these ideas have scary consequences, whether Pianka has drawn those consequences or not.