I have a strong aversion to waste. Unwanted mail is wasteful of paper, printing, postage, etc.

It probably has to do with being raised during the (all-too-brief) era of what Kestrell refers to as "The crying Indian" public service announcements during Saturday morning cartoons.

Also factored in is the time I spent at (IIRC) DSP, where my job was removing useless addresses from a marketing database. I have firsthand experience of how much marketing departments want to remove these things.