I still remember my Biology 101 Prof explaining why he felt (strongly) that psychology was a pseudoscience.
I imagine this question to me is b/c of my thread about my TOP 10 changes I would make in the US. Here's the thing...
Yes. There is error in psychological testing. If you and I were candidates to go on a mission to Jupiter, would a psychological test be fool proof to differentiate between the two of us? Probably not. But, that's not my point.
My point is to differentiate the people who suffer from TRUE mental disorders from those that do not. Manic/depressive, schizophrenia, paranoid personality disorders etc are very real and one sees them in ER's on a daily basis. And, then there are people victims of child abuse, etc that can be brought to light, as well as other developmentally delayed individuals, too.
This is why I support psychological testing.