Please not another poll... Frankly I tend to agree with you... that those behind us have the reponsibility.
However... "behind you" is a relative term when sharing lanes, or when moving laterally (to make a turn) as you are now moving into a location where there was nothing before...
Consider this. While a motorist does have responsibilty to watch out for traffic directly in front, if another motorist suddenly changed lanes in front of the first motorist, would the lane changing motorist be allowed to get off scott free?
Maybe... or they may be handed a reckless driving ticket.
In the case of autos however, there was a clear delineation based on different lanes... that case may not exist in the case of cyclists sharing lanes.