I think it’s important to realize, the mice are still dying as we speak for this purpose.
This is simply a step toward not needing to literally kill animals needlessly, if it succeeds. In the meantime, while stuff like this is really early on, we’re not going to stop animal testing.
I think for most people who are against animal testing it is not the death of the animals that is the principal problem, it is the suffering they undergo while alive.