Due diligence: the care that a reasonable person exercises to avoid harm to other persons or their property

research and analysis of a company or organization done in preparation for a business transaction (as a corporate merger or purchase of securities)

http://www.merriam-webster.com/dictionary/due%20diligence

If I go grab a report from the National Enquirer and paste it on a discussion board and then make a series of subsequent posts about how irresponsible and incompetent an entity must be if the report proves to be true, would you define that as me doing due diligence?

I would argue what you did is completely contrary to the first part of the definition above.