I'm not sure why anyone would give you a dislike for this - you're absolutely correct! The idiom itself is emphasizing the individual (hence every one) not the group (everyone). In this particular idiom the two words should always be separate or the idiom just doesn't retain its true meaning.
Fun fact! I've had several native speakers tell me that "iskrem" is not used when referring to ice cream and it is just shortened to "is". When I asked how they differentiated it from regular ice (cubes) they explained that it was referred to as "isbiter" or ice pieces/bits. Cool, huh? ;)
same in german actually. well. we call them Eiswürfel which is just the literal translation of ice cubes. We say "ice" (Eis) to both, ice cream and ice in general. You can differentiate by the context. "I want an ice" would refer to ice cream and "I want to go onto the ice" refers to ice on a lake.
Random question - I've heard that Norwegians don't really refer to ice cream as iskrem, but they usually call it is. How do you distinct between ice cream (which we would generally assume is in a tub) and AN ice cream (which we assume is on a stick/cone). Is it as simple as using the definite article?