You did. By saying you focus on PC weaknesses you're choosing to metagame deliberately to punish players for character choices. I consider that an abuse of DM power and responsibility. Now, if you're turning around and restating your position by saying you don't do it deliberately and simply include all aspects of the game as an organic construct then that's a different story and the responsibility falls back to the player to manage the consequences of their choices.
But I stand by my assertion that deliberately punishing players for mechanical weaknesses in their PC's in order to "balance" a game is immoral.
You keep using that word. I do not think it means what you think it means.
But, in any case, umm, why wouldn't you challenge your players this way? If the players choose to hyper focus on X which results in weakness Y, why would you not exploit that in order to make the game more challenging? Isn't this pretty much basic DMing 101?
What's the alternative? We only design adventures that fall squarely in the player's wheelhouse? Every encounter can only be designed in such a way that it plays to the PC's strengths and never their weaknesses? Now, obviously there are all sorts of shades of grey in between here. Some encounters should play to the PC's strengths - let them be the Big Damn Heroes is pretty cool. By the same token though, some encounters should play to their weaknesses as well.
If you have a player who creates a one trick pony character, do you automatically design scenarios that play to that character's strengths? How is that not just as meta-gaming? Encounters should be complex enough that strengths and weaknesses are targetted, shouldn't they? So, you have a PC that goes the Great Weapon Master Raging Barbarian route, does that mean I can never use ranged combatants? What about the caster that hyper focuses on, say, a single element like fire spells. Does that mean I can never use monsters that are immune to fire?
Are you seriously suggesting that it's actually
immoral to use fire immune creatures in this case?