As the Williams Institute points out these are outcomes based on parenting from ten to twenty years ago. The study looked at people who were raised during a time when same-sex unions were not as widely accepted as they are today, the study could be labeled a snapshot of a time that has passed.
As Pink News details:
Dr Regnerus [the author of the study] agreed that instability in the lives of those who took part in the study was a more likely culprit for negative outcomes in adult life, noting that given the age of the participants, they were more likely to have been born into a straight relationship which broke down than they were to have been planned children of gay parents.This study is published in the Social Science Journal which is published by the Western Social Science Association (formerly known as the Rocky Mountain Social Science Association). The editor of the journal is out of Colorado State.
He said organisations might use these findings “to press a political program. And I concur that that is not what data come prepared to do [...] Implying causation here—to parental sexual orientation or anything else, for that matter—is a bridge too far.”
The most prestigious scholarly publication in this area is Social Science & Medicine whose editors are Ivy League and international scholars of considerable note. They provide peer review guidelines that are very informative and interesting.