Justifying one thing because it's a necessary component of another unnecessary thing... what logical fallacy is that?

That's old fashioned rationalization.

Doesn't necessarily have to be a logical fallacy

Can you elaborate?

I think you mean false premise or argument from false premises. "A, therefore B", even though A is false.

Post rationalization perhaps?

It could also be similar to the logic of phrenology, where they pointed at objective measurements of various features of people's skulls to make wild conclusions about the superiority or inferiority of different races. It's not that they were falsifying the measurements, they just skipped a step and treated the sensibilities of the most privileged and influential members of society as objective fact.

Unnn... the whole is greater than the sum of the parts?

Depending on the circumstances, it can be effectively justified. wordle hint

Logical fallacies do not involve themselves in questions of worthiness, usefulness, goodnesss, etc.

If the fallacy relies on this pattern of detecting necessary and unnecessary, then it is not a logical fallacy.