Another important thing to remember (or forget) is that commemoration need not be a marker of praise. The word "quisling", for instance, means "a traitor to one's country" (OED 2007). It is derived from Vidkun Quisling (1887-1945), the so-called Minister-President of Nazi-occupied Norway. During the war his surname became synonymous with treasonable behaviour. Its use as a noun occurred first in The Times newspaper’s article entitled "Quislings everywhere" (15 April 1940, p.5).
Quisling is a less familiar word today, but it still has currency. It could quite legitimately be used in reference to Anders Behring Breivik (born 1979), a Norwegian whose extreme right-wing beliefs led him to murder 77 of his fellow citizens on 22nd July 2011.
OED (2007) "quisling, n. and adj." Third edition, December 2007; online version June 2011. <http://www.oed.com/view/Entry/156777>; accessed 11 August 2011. An entry for this word was first included in A Supplement to the OED III, 1982.