It's also in the same carcinogen group as electromagnetic fields, aloe vera, nickel, and kimchi. Most of those things you listed are quite dangerous for other reasons, but cancer is not the primary concern with any of them.

IARC group 2B is where substances end up if a study manages to produce cancer at any dose. If you drink 50 cans of diet coke per day (which is the equivalent of the rat study that demonstrated that it's possible for aspartame to cause cancer), then you might get cancer caused by the aspartame you just consumed.