From Wikipedia "Law 32/2007 provides that the government will take measures to ensure that farm animals are not caused unnecessary suffering, and was enacted in order to comply with European Union requirements on farm animal welfare. " https://en.m.wikipedia.org/wiki/Animal_welfare_and_rights_in_Spain so while this law doesnt address farm animals other laws do. I cant comment on application or enforcement but it is usual to have different laws related to farm animal welfare and domestic animal welfare since the issues are often different in each case.

Im not familiar with the case but generally in constitutional states if a law is ruled as unconstitutional then it is treated as if the law never existed (since it has been found to be invalid) therefore all convictions based on it are considered invalid. This is different to a law being repealed (which the original post refers to)

Your argument has a point but we are not talking about just fuels. You are right in that the energy would be most efficiently used to avoid extraction of more fossil fuel but..

In this case we are reusing plastic produced from Oil rather than discarding it. We have a large stock of plastic that we have no use for. Do we bury it, burn it (releasing CO2) or can we reuse it?

Re using this as a substitute for fuels or plastic feedstocks that have no ready sustainable replacement reduces the net amount of carbon emitted. Ideally we would have substitutes for every application but we dont yet (Jet fuel being a good example but we also dont have good substitutes for many plastics either) so these provide more pathways for non-polluting energy to be added to the mix.