Point 1 is wrong, unless the person drafting you is on the back of your tandem. On a normal bike, they are too far behind you to assist streamlining.
Well, I was never around when those folks were crunching the numbers in the wind tunnel, so you'd have to take it up with them.
I'll agree with most of the rest but I tend to have a little more concern about not deliberately taking down a wheel sucker.
I guess there's still enough racerboy in me that I take an exceptionally dim view of wheelsuckers. I would never suggest intentionally taking down another rider, though -- unless they're not using Campy or something, of course -- but if they should happen to run into that brick in the gutter that you just hopped... Just kidding. Sort of.
Don't see why people get bent out of shape over people sitting on your wheel for long periods though. Just slow down, ride beside them and engage them in conversation.
In all seriousness, I agree with this completely. At the very least, the wheelsucker isn't costing you anything, as long as you can get over any feelings of obligation toward your uninvited guest.