Wolfspider said:
If you want to look at it that way, EVERY rule in the game is optional.
Minions are barely even a rule, though. They're a monster manual entry.
Rules are "there's rule 0 i guess" sorta-optional. If you change a rule, you'll have to explain it to the players.
Monsters are actually optional. The DM has to specifically choose to use them. Omitting to use minions, or carrion crawlers, or flumphs, or whatever else, is noncontroversial, and I've done it with at least 50% of the previous monster manuals.
I still think it's valid to discuss the effects of a particular rule, its strengths and weaknesses and ramifications.
A bad rule is one that provides a worse playing experience for the players. I think very few players are going to find their experience hurt by the fact that they killed some creatures in one shot. Things being killed in one shot is perfectly consistent with both literature and the real world.
For the DM, an orc minion and an orc warrior are creatures of fundamentally different types.
For the player, (assuming the orcs look the same) they're both Schroedinger's Orc, existing in the state of "minion" and "nonminion" until their status is determined by observation (here, as in all good science, observation is done with a giant axe or an explosion).
If you didn't have minions, then with the 4e HP model, you would very rarely kill an appropriate-level creature in one hit, and that would, in my mind, start to damage "verisimilitude" and start to make combat feel samey. I have simulationist tendencies, and leaning towards frequent use of minions.