Avira,
I agree with you that being rachman to the cruel with lead to the opposite, etc. And have no problem with your example on competition and innate desire to defend. I don’t think though that the choice is usually that sharp. I often see gratuitous rudeness as an expression of Judaism, when one could simply discuss the underlying issue instead of focusing on personalities.
Mussar teaches us to verify personal biases. Example: R Meltzer was not sure whether to write a recommendation to a student. He wrote it and then threw it away. Why? He was afraid that a consideration of saving time/effort was affecting his decision. If such a refined person questions his own judgment, so should we. So, if I or you have a tendency to judge people or groups of people, then you need to double-check before coming to a conclusion.