Noise is one reason, but your car crash reason is rubbish - OK, accidents tend to be more spectacular, but traffic is all going in the same direction on each lane and they are much safer that normal town or country roads.
Bad things - people have to move out if homes or farmland are compulsorily purchased; embankments and cuttings have to be dug out or built, spoiling the view - interchanges are massive constructions; wildlife suffers (find a bunch of rare snails or rare voles, or orchids, who will die if it's built); light pollution as well as noise, from motorway lights, especially at interchanges (when did you last see the stars, without artificial light affecting it somewhere?). your argument needs to be about the environment, not safety. Do the public want it, find out the reason it's being proposed, and argue against those reasons.