ScourgeOfCorruptor
Terrarian
As a lot of people play one class playthroughs, why not make it an official part of the game? It could give you special bonuses and rewards as well.
It's meant to be as a fun challenge that is optional, much like expertmode or medium/hardcore.Classes like Summoner aren't meant to be played as one class only.
They can always try, and then later notice how difficult it is, but that's because they wanted to limitate theirselves.