Ha, the strawman! Clever.Teach any strawmen?
If STD has a cast of hundreds or as many students you have taught then of course there will be plenty of volume with which to represent every circumstance. It won't.
Trying to represent every possibility over maybe a dozen characters? That strains believability.
It's the reality of our world and the fictional world we are talking about. It's not an unbelievable scenario that a society (the Federation) that represents trillions would be extremely diverse. Even in this world, if we picked 12 people randomly, those 12 people would be far more diverse than your standard hollywood or tv production. But I guess it's easier to argue "checklist!" and "social justice warrior!"
Representing diversity is not a checklist. It's a fact of life.