IMHO by far the best weapon is the unvarnished truth and the pure and simple fact that "Speed Kills" campaigns have failed.
I have presented the evidence from New Zealand here and it is quite uncontestable:
http://www.fastandsafe.org/site.aspx/Pages/Facts/TicketQuotas/index
Speeding fines are up exponentially, average speeds are down, but fatalities are
up and injuries
hugely up relative to the rock steady decline for the seven years prior to introducing hardline policies and expanded patrol activities in 2001.
I would like to see the same data presented for other countries involved in the "Speed Kills" catastrophe.