I'm not an idiot (well, not completely at least), and I realize that non-profit, not-for profit, etc. organizations, causes and charities rely on repeat donors in order to sustain themselves. It makes sense and I don't knock them for it.
However... there is a constructive way and a counterproductive way of doing this. For instance:
I give blood or platelets 3-4 times a year and have done so for the past 8 or so years. This is because I am the ideal image of philanthropy and a stalwart for humanitarianism. So when the Red Cross started calling me four times a week I tolerated it for a few months. But even Ghandi had his limits. I finally had to call and explain to them that as much as I support the cause, I don't particularly enjoy having my veins prodded and jabbed at and (eventually) opened by your undertrained and oft-incompetent blood collectors, and I think once every three months is generous enough and that moreover, I am nearly certain that Dracula himself would be less pushy about such collections. I felt somewhat bad about laying down my fist on blood solicitation but the Red Cross's guerrilla campaign left me with little recourse.
Another thing that really chaps my ass is when you open your checkbook to an organization (such as the Human Rights Campaign), and as a token of their appreciation they sell your info to other folks. I cannot even begin to scrape the surface of how unbelievably slimy this is. The most evil aspect of this scenario is that groups to whom you have "voluntary" disclosed your info are exempt from the no-call and no-mail lists.