The upshot is, vocal Wikimedians on mailing lists hate banners, and are quite willing to sternly lecture about their dire consequences! It's left to the Foundation, then, to choose between large numbers of donations from happy donors and unamused mailing list participants. Tough call.
My own opinion closely mirrors that of Michael Snow, so I'll quote what he said..
I'll agree with this as well - and add that, having seen many organisations' fundraising, the Wikimedia fundraising team goes to exceptional lengths to listen to community views and make sure that its work provides a great user experience. Keep up the good work!
Chris