Yes, like I said, it's not perfect. There will still be deepfakes, but they won't be around every single nook and cranny. And once you ever invalidate a video, all other works by the same key are now suspect.

Imagine two court cases. In one, there is a video signed with a key from a phone that shows no signs of compromise. In the other, there is a video with no signatures at all. Which is more trustworthy? It's a continuum, not a binary.

Edit:

And also, we can scale trust. There should be more webs-of-trust in the world. I should be able to tap my phone next to my buddies and it should create a link between us. We should have the concept of trust online when we need it.