It's a valid question. The article takes the following premise: Parapsychology gets positive results following the scientific method as defined by prevailing norms in the scientific community. So why can't we draw the conclusion that parapsychology is as legitimate as other branches of science? What is to separate it?

I would offer a pseudo-Bayesian[1] answer to that question. Parapsychology aims to prove hypotheses that lacks theoretical foundations. Our current understanding of physics and biology weigh strongly against the existence of psychic phenomena. Even before any experiment is conducted, we must admit that psychic phenomena are unlikely to exist. Our experimental results must be evaluated in light of that prior probability.

Thus, parapsychology is and should be held to a higher burden of proof than other branches of science. We should demand more rigorous experimental designs, stronger effects, and smaller p values. This XKCD presents a similar idea, if you substitute "psychic phenomena exist" for "the sun has gone nova":

http://www.explainxkcd.com/wiki/index.php?title=1132:_Freque...

[1] I say "pseudo" because I'm not a statistician by trade. I'm basing my argument on my rather superficial understanding of Bayesian statistics. I still think it's a valid argument in its own right, but I don't claim that it's an accurate representation of Bayesian statistics.