@tb
I am of the 'if you kill Hitler someone else will do what he did' school of thought. I think in patterns rather than coincidences. It is fun to reduce historical events to that one pivotal moment ?, but in almost every case that pivot was bound to turn soon anyway.
I think we can (and should) change the present, but i think that is way to hard work for any timetraveler to accidentally screw up.
The future does not change because i accidentally stepped on a butterfly and caused a storm, the future changes because we collect thousands of butterflies and make that storm happen!! ?