It’s not comparing him to Hitler. It’s pointing out that everyone has a line where killing them is better than not, and Hitler is the extreme example that everyone should agree that killing him is better. It isn’t making the case Kirk is past that line for everyone, but pointing out the idea it’s never allowed is stupid.

People can debate whether it is worth it in this case if they want. However, the thought terminating cliche that it’s never acceptable should be ignored. Pointing to Hitler is a good way to dispel that idea for people.