You didn't mention his airspeed however, I'm turning 30 degrees and descending until he passes. It costs me nothing.
How do you know he is not about to initiate a descent??? If he's high performance he could be in your flight path in seconds.
How do you know both readouts are precisely correct? Technology is not perfect.
It costs nothing to make a slight deviation.
Let's put it another way. Without the technology, if you see an aircraft at 12 o'clock and three miles on a converging course, would you make a deviation? I'm guessing you would because that 500 feet is very hard to judge, and again, you don't know if they are about to descend. I'm guessing without the ADSB input, you are going to deviate.
I understand that some people fly as if nothing bad is going to happen to them. My perspective is about the opposite.