I've been considering buying a bird feeder to amuse my cats, but you're right. I'd never considered it. I feel very strongly about not feeding wild animals when I hike, and from a bird's perspective a feeder is the same thing.
Maybe find which flowering plants attract the most hummingbirds and butterflies in your area and plant them under the window. Entertaining and beautiful. Recommended species by state: http://www.wildflower.org/collections/ It is more work though.
To be fair, it's been a part of our culture for all these years so it's something that's normal for nature lovers to want. Also, on the scale of things, it's probably a lot less damaging than say purposely keeping your trash cans open so the raccoons can feast whenever they want. So I'm not gonna disparage anyone who owns one or wants to own one. But on the other hand, we used to promote feeding wildlife at our national parks and over time we learned how unhealthy that was. So, I mean, we have to at least appreciate the fact that communal feeders can have a negative impact on birds.