I hear you, and by that logic, you also shouldn't trust McDonald's, Wendy's, Arby's, Chick-fil-A, Starbucks, Sara Lee, Pizza Hut, or the nearly 500 other mainstream food products that used this FDA-approved ingredient. Subway actually removed it ahead of many competitors.
The FDA approved azodicarbonamide as "Generally Recognized as Safe" and it's still legal in the US and Canada today. Almost every major food company was using it at some point—it wasn't some rogue Subway decision, it was industry standard practice.