"This criticism is about the application of the principle, not automatically about the person's motives."

First, let's distinguish application from motive.

Application = how someone actually uses a principle in particular cases.

Motive = why they use it that way (their intention or purpose).

These are logically different.

Example 1

A judge says:

"Freedom of speech should be protected."

He protects speech in Cases A, B, and C, but not in D.

A critic asks:

"Why is D different?"

The criticism is initially about application:

"Your principle doesn't seem to be applied consistently."

It does not yet prove the judge's motive.

Perhaps D genuinely involves incitement to violence, making it legally different. Or perhaps the judge is biased. The inconsistency raises a question, but by itself it does not conclusively establish the reason.

Example 2

A historian says:

"Only contemporary documents should be trusted."

But then cites medieval chronicles when they support his thesis.

Again, the first criticism is:

"You are applying your evidentiary rule inconsistently."

Whether this inconsistency results from oversight, methodological error, or deliberate bias is a further inference requiring additional support.

People wrote:

"I think application tells conclusively about motives."

Sometimes repeated patterns of application can provide evidence about motives, especially if no plausible alternative explanation exists. But logically, they do not establish motives conclusively.

For example:

Inconsistent application may indicate bias.

It may indicate carelessness.

It may reflect an unstated distinction between cases.

To conclude motive, you need additional evidence showing that those alternatives are less plausible.