Tech is such a malleable thing. Let's say that this repo doesn't exist, but repos exist for doing facial tracking on webcam feeds and pictures (for facial recognition), and others for modifying a 3d model according to a facial model output by facial trackers (for 3d avatars).

Let's say that the tech around this DeepFaceLive repo develops to the point that the repo can become just a 10-line file of glue that makes a 3d model that's just a grid plane with a picture on it that moves according to a webcam feed. Such a repo is redundant and anyone that wants this tech can just apply the repos mentioned in the previous paragraph to do the equivalent.

Are those repos now bad? If not, it seems the ethical question can be resolved by some restructuring of code so bad uses are not made so obvious, while being almost as easy.

What technologies are fundamentally bad? I don't know of any outside of perhaps torture devices.

You're opening another can of worms with that example. An adult, informed smoker that takes care to not cause second-hand smoking and that doesn't have any dependents, causes harm only to themselves. If they think that the reduction of stress or whatever else they gain at the tradeoff of their health is worth it, that's their choice. That's part of their bodily autonomy. As such, the tech is still not inherently bad.