Lots of others think comments like that indicate he's a wingnut who has been brainwashed by X.
Personally, I turn off most comments like that because there's no substance behind, "... is the worst in history!!!!11!!!" I think too many people who make comments like that don't know enough about US history to make such a comparison. Or if they do know the history, the don't respect their readers enough to present the evidence for their views.
For instance, on the corruption side, I haven't seen a comparison of GWB's administration with [link|http://en.wikipedia.org/wiki/James_Buchanan|Buchanan's], [link|http://www.u-s-history.com/pages/h234.html|Grant's] or [link|http://en.wikipedia.org/wiki/Warren_G._Harding|Harding's].
On the senseless war side, how about a comparison to the [link|http://en.wikipedia.org/wiki/Philippine-American_War|Phillipine-American War] or the [link|http://en.wikipedia.org/wiki/Spanish-American_War|Spanish-American War]?
:-/
Cheers,
Scott.
(Who thinks that GWB has done great damage to the country but doesn't know how he would rank him on a particular scale because he thinks that such rankings are generally meaningless.)