The strongest conclusions from Rat Park should be that rodent studies are complicated by lab conditions. This probably doesn't sound too controversial (by now anyway). But because of the ideological or personal issues at play, it's easy to draw conclusions about humans from Rat Park.
Put another way, placebo studies show that attention and treatment alone get some level of result and that science is hard, not that sugar pills are a panacea.
Rat Park is an excellent example of how people pick studies that show the things they're looking for. When people point to it uncritically, it says more about them than about the world.
I was providing the link as context and a jumping off point for further reading, if you were curious (which is encouraged here). If you're looking for criticisms of Rat Park, I suggest starting with the "Criticisms" section on the Wikipedia article.
Put another way, placebo studies show that attention and treatment alone get some level of result and that science is hard, not that sugar pills are a panacea.