I don’t want my site to enable users to get tracked by gravatar. Googling for “what is gravatar’s business model”, the very first link I get is https://www.quora.com/What-is-Gravatars-business-model-How-do-they-stay-profitable, which seems to be about tracking which I find unethical, and I don’t want to help enable it through my discourse installation.
A bug report means something is broken, preventing normal/typical use of Discourse.
As to your request, there is not currently an option to fully disable gravatar. You can disable the
automatically download gravatars site setting, however, so your users would need to make the explicit choice to enable Gravatar for their account, rather than it being automatic.