There's an interesting hypothesis that the pathway to cancer for aspartame (if it exists) might involve creating formaldehyde in the same way that's done when drinking ethanol, and so actually, drinking alcohol is _protective_ as it blocks the aspartame cancer effect -- in a similar way that ethanol is a treatment for methanol poisoning.

I don't really worry about aspartame cancer risk though, it doesn't seem like a big deal if it exists at all. I do buy the idea that diet sodas kill good gut bacteria and avoid them for that reason, but I don't remember a single thing about where I got that idea. It just "feels" right, and I don't mind the lack.