This is not some kook; this is the dude who ran the Viking experiment in the 1970s.
I agree with him, though I am no expert, and here’s what I think is going on: NASA does not want to know if there is life on Mars because that opens up all sorts of issues about the ethics of exploring Mars, of even visiting that planet in the first place. If we find life there (and I suspect we already have) then that drastically alters our future efforts in exploring the planet, other planets and moons (such as Europa, where life is also possible) and of course leads to questions about our place in the larger universe.
And NASA, as much as I love it, is a government agency. Discovering (or admitting to the discovery) of life on Mars changes the status quo enormously, and most of all government agencies do not want that. That’s why there have never been any more experiments designed to detect life, and probably never will be — at least not from NASA.