I'm not in that debate at all (this was actually the first time I heard there is an "anti-daycare movement" at all) but I found the section on cortisol to be extremely unconvincing.

Basically, the anti-daycare camp claims they have evidence of a clear relationship between elevated cortisol levels and daycare visits - to which the author responds with a bunch of irrelevant, deflective points like "cortisol is an important part of the metabolism and it fluctuates all the time anyway and sometimes it's even low in people who are stressed!" None of which addresses the concrete issue that the camp brought up.

That's "the climate has changed before" kind of arguing.

The irony is that he made a better argument at the end ("are they really stressed or just excited and in an unfamiliar environment, meeting lots of new people, etc etc") but only after doing all this handwaving before.