Originally Posted by
Frontier
I can't think of a gangster who would unironically call themselves The Joker, at least the way Joker actually uses his name.
Captain Cold fits his powerset and his role within Flash's Rogues Gallery. The comics have been taking him seriously for years, as has the TV show. Fans would complain a lot if you treated him and the rest of The Rogues like jokes.
I don't see how The Flash can't be taken seriously any more then other Superhero properties, especially when there is so much heart and stakes set in every story.