This is something that a lot of people claim with a universally authoritative tone, but it's counter to my own experience. I don't consume regularly candy, sweets, etc., but I do drink diet soda and zero-sugar energy drinks and when I (rarely) have fruits or make mixed drinks with fruit components they are really sweet to my palate. When I've cut diet soda out for long periods, fruits taste no sweeter. Cooked starches and tubers are already sweet-tasting and always have been for me; diet soda doesn't affect those, either.

Moderation might not be fine for you. It seems to work for me.