People are not concerned about that. If we tell them that they must fill out the questionnaire because it will help them and make their needs known in order to better address them, they will do it. If we tell them to fill it out, but that we don't know what it will be used for, they will not care as much. It is different if they really know why they're filling it out.
I still don't believe that it is an invasion of privacy. If someone does not answer question 33 because they don't find it appropriate, but they answer all the other questions, data will still be collected for all those other questions.