I don't know about this questionnaire(and I don't have enough time to check right now), but similar ones are quite reliable tools for self-assessment. They are _designed_ to be used without presence of mental health professional, and they work. Most of your criticism is valid though, and scores may be distorted, but I am quite skeptical that this effects leads to many false positives.

Also, I am not saying that criticising yourself is not normal, I'm saying that spending all time criticising and blaming is not normal.

By the way, if your score actually more than 10, try other tools, Beck Depression Inventory for example. And try reading the book, you may find it useful even if you aren't clinically depressed. BTW, there is a chapter on perfectionism(which is quite common attitude in depressed individuals).