How can researchers weigh the need to conduct research against the need for ethical procedures?
I would argue that there is no "weighing" to be done in this day and age. Whenever there is research to be done on human subjects, the need for ethical procedures must come first. This is true both for ethical reasons and for legal reasons.
Of course, there are many types of research that social scientists might like to do that are impossible given the protections for human subjects. However, there is no process of weighing the possible importance of the research against the rights of the subjects. In this area, the rights of the potential research subjects always trump the desire to do research.