I'm for changing the system from "do animal testing unless you can prove you don't need it" to "do it if you prove you do need it"
The problem I see is that many drugs/compounds etc atc differently on animals, even primates. So if we test on animals where there is no correlation between test and human affect:
1) Places false confidence in drug, risking humans (cases seen where drugs tested fine on animals, hurt humans)
2) Suffering for no gain
3) Makes drugs more expensive due to high animal testing costs (have to do human trials after)
4) Less investment in alternatives, like lab grown flesh etc
5) Diminishes faith in science.
So by changing to opt-in, provides a liability shield for pharma, currently a big consideration is to do animal testing so if there are human issues, can't get sued (even if it didn't help or worse).
Then for the cases (basic toxicity as PTAO) that merit it, we keep it.
Of course due to extreme opponents many in science (understandibly) have a siege mentality of protecting all testing because it's all worth it