Sorry to come in at the end of this but I've only just joined the site. Interesting debate and one that is persistent in the world of photography. One consideration, which I dont think has been mentioned above, is under what conditions the event was staged. It sounds like it may have been a rally club event. On some events where the public is admitted, for a charge or not, by simply entering you may be agreeing to the organizers Terms and Conditions, and I have seen many that prohibit the public taking photographs, even on public land.
However, if it what could be described as an open event, no admittance process, no restriction on movement in the area the event is being staged and no warnings and it is on public land or land that has open access then I would suggest then organizers can not do a lot about it.
I would ask them under what conditions they are asking me to take the images down or selling them.