[tjaerv]

"One of the bylaws of the International Association of Time Travelers states that you can't kill Hitler. The problem is, everybody kills Hitler on their first trip. This leaves more experienced time travelers the onerous task of undoing the historical edits of n00bs."

http://www.tor.com/stories/2011/08/wikihistory

[afterburner]

That's hilarious, but the justification they give for not killing Hitler is unfortunately pretty weak:

"no Hitler means no Third Reich, no World War II, no rocketry programs, no electronics, no computers, no time travel."

But still worth a read!