"It would be cost-prohibitive not to litter"

If one can't do business without carelessly leveraging finite public resources I would argue that that business is untenable

Untenable only in a stable-state eco/technological culture. If, however, the technological culture of which satellites are a part is able to bootstrap itself through behaviors that are only viable in the short term, and burst through to levels of capability that are long-term viable and can rectify the short-term behaviors that came before, then everything can work out alright.

I know, I know, the above is close to hopelessly optimistic. It's like when I was younger: I remember thinking, "I'm not going to smoke cigarettes, but if I did it would probably be okay. By the time it would really matter, medicine will have surely found cures." I was an idiot, though I never did smoke.

This is the type of judgmental comment/rationale that we hear around climate change as well... 'if humanity never knew how to do it properly - considering forseen and unforseen circustances - we should never have done it'

Public resources are always consumed while public exists. We should thrive to always experiment, learn from it and evolve/do better.

Something like that suggests it would be good to step back a bit and rethink things. So why is litter bad? Litter is usually regarded to mean disposal of trash consisting of manufactured goods in natural areas, such as parks, forests, oceans, lakes, etc. It's considered to be bad because it's visually unsightly to humans, may interfere with wildlife in various ways, and may result in various types of toxic chemicals leaking out into the environment.

When we're talking about satellites in graveyard orbits, no humans can see it, there's no wildlife, or really any environment to damage. None of the concerns we have with litter apply. Trying to speak against it as if it's litter is then either an attempt to shoehorn a concept into a place where it doesn't apply to make a snap judgement, or a malicious attempt to attach something for other reasons. No comment on which is going on here, but if you're going to convince anybody not to enjoy the many benefits of geostationary satellites, you're going to need to make a better case than likening it to "litter".

Do you hold graveyard orbits located 11m/s above GEO to be an inadequate or irresponsible way of preserving the integrity of GEO?

Not cost-prohibitive. Just cost. Devoting 5% of the mass to an ion deorbit thruster wouldn't be particularly hard.

How long would that take to deorbit? Don't want junk slowly drifting through every other orbital path on the way down, either.

A single digit number of years, I think. Not too bad, especially since you can control its path.

Why is it higher, rather than lower? If it is higher, will it not eventually be back in geostationary orbit?

At these orbital heights, there is no atmosphere for drag effects, so adding energy to move to a slightly higher orbit, outside of true geosync altitude, is a permanent change.

Low Earth orbits do have atmospheric drag issues, and those items need to have fuel to replace lost velocity and restore the correct orbit.

The ISS page has a neat table of orbital height over time where you can see the burns to 'jack it back up'.