It's widely recognized now that even if all negative effects can't be avoided, they should be anticipated as fully as possible through impact assessments that include technological, environmental, and social effects. To fail to do this leaves society subject to unintended human, social, and environmental costs and sometimes irreversible consequences that are more severe than the original problems that prompted the action. In addition, the various groups having an interest in a study are likely to be unclear about what the potential problems are. Thus, the initial framing of the problem may require frequent reworking. Therefore, it's impossible to identify a single general methodology applicable to all potential impact situations.
Several conflicts are inherent to impact assessments.
These conflicts are political and usually call for public policy education. One purpose of an impact study is to make these choices known. The choices obviously aren't all technical, but are value-laden and political as well. They reflect social goals. Political issues are at stake among special interest groups, organizations, government, the general public, and those trying to represent future generations.