Sodium benzoate in soft drinks reacting to produce benzene?
The reaction taking place is described in article Benzene production from decarboxylation of benzoic acid in the presence of ascorbic acid and a transition-metal catalyst and its importance for food safety recently reviewed in Evaluation of Accelerated UV and Thermal Testing for Benzene Formation in Beverages Containing Benzoate and Ascorbic Acid.

To summarize, the reaction CAN occur, namely at elevated temperatures (>50 °C) and UV-light and in presence of transition metal. Even if the reaction takes place, the amount of benzene formed is either below detection limit, or below limit for drinking water.

For the end user it means, that in extremely unlucky situation, the benzene can form in quantity, which is not considered safe to drink in unlimited amount for the whole life (1 ppb). As such, I would consider the benzene formation as very weak argument against such beverages (mainly if compared with other problems, such as sugar content and associated obesity).