This policy has been in place for decades with no change. That makes me doubt it effectiveness. I've heard of plenty of USA -> BR travelers being turned away at the border because they didn't realize they needed visas (a common occurrence for people traveling for conferences). Ultimately they understand the reasons and even empathize with the country, but it doesn't change the fact that for them it's easier to just not come.

To me it's more about an ineffective, vain attempt to show power than anything else.