"If the author applies the principle only where it supports one preferred outcome..."

This concerns consistency.

Suppose someone proposes the principle:

"Present stewardship should determine territorial rights."

There are two possibilities.

Consistent application

They apply it to:

• Kashmir
• Gaza
• Crimea
• Northern Cyprus
• Western Sahara

whether they like the political consequences or not.

Then readers can evaluate whether the principle itself is sound.

Selective application

They invoke it only where it supports the political outcome they already favor, while abandoning it elsewhere.

Then critics can argue that the principle is being used selectively rather than consistently.

Notice that this criticism is about the application of the principle, not automatically about the person's motives. Someone may sincerely believe there are relevant differences between cases, but they should explain those differences.