How do you feel about external countries dictating your government policy? Often this won't go the way you want.
Is Mercosur unpopular in Brazil? Eliminating it would be quite costly to the world.
I don't see any chance of this not going bad. It would set the climate to somebody much worse than Bolsonaro to get into power. I don't see how the GP could ever want it, but there is a small and loud political movement that does ask for it.
(By the way, Mercosul is popular in Brazil. Preserving forests is too. Preserving non-forest biodiversity is less popular, but as soon as people see the choice, they like it. All of those have strong opposition from small groups.)
I believe it's a fair statement. If you come in with economic sanctions with policy in mind. You have dictated what that policy is. There's no beating around the bush.