Psychology practiced by amateurs

I just ran across this Justice Scalia quote:

But interior decorating is a rock-hard science compared to psychology practiced by amateurs. A few citations of "[r]esearch in psychology" that have no particular bearing upon the precise issue here, ante, at 593, cannot disguise the fact that the Court has gone beyond the realm where judges know what they are doing. [Lee v Weisman, 505 U.S. 577 (1992)]

No, he was not talking about a family court judge trying to make a custody decision.