We all subscribe to newsletters we mean to read and then don't. And then we transfer that feeling to our readers and worry they've done the same thing. I combat that by regularly asking folks to unsubscribe. (And if I discover I'm not reading a newsletter, I unsub myself. There's only so much time. We can't do it all. What we cull is as important as what we keep.)
Telling them it's okay to leave helps cull the folks who are staying because they're too nice to unsubscribe.
Everyone is busy. I see the choices as (a) be easy to ignore, and become One of Those Newsletters, or (b) be so good they don't want to ignore you.
Yeah, (b) is harder. It's also the professional choice.