When I first set up isso, I had a hell of a time getting it configured and running, following the pretty poor official documentation. So I visited the Github repo to ask for help but, after seeing the dev's condescending attitude to other people in difficulties, I thought better of it and [fortunately] managed to muddle through by myself.
So you tell them to go use Disqus if they need Gravator since they're basically stating they don't care about anti-tracking.
You then also state that someone else should do the work of integrating with Libravator.
It reads a bit gruff and asshole-ish.
On the other hand, TANSTAAFL and either someone should pay you or do the work to do the Libravator integration, and it does seem very odd to pick up Isso and then want to use an avatar service that also does tracking.
Presumably those people hate Disqus for other reasons, but it certainly doesn't have to be your concern.
I'd probably write the same kind of tone in a FAQ entry as well, because if its being given away for free then the flip side is that users on the internet shouldn't be demanding assholes and want things for free that you have zero interest in providing for free, and I think you make your position reasonably clear.