A significant part of the player base like them. It feeds from movies books etc. just because non thieves can steal doesn't make the idea of organized thieves (AKA the DND Mafioso). Invalid. Normal people steal secrets all thetume does that invalidate the idea of intelligence agencies or corporate counter espionage teams.So with a great deal of systems, I see a dedicated profession of thief. I would argue the need on the basis that, thieves do not have special powers, just skills. You could play a warrior, and rob people, take advantage of someone you caught off guard, a servant could walk away with important documents, or a locksmith could open locks. Debate me, and if you like thieves, what do you like about them?
Anyone can pick up a sword and stab someone. Do we really need the profession if Warrior? . Your thin logic cold be used to justify a classless game. Perhaps something like GURPs is what you are drifting tówards