There are plenty of cases where immigration can be negative, particularly in the short term, so controlling the amount of immigration makes sense.

In the case of corn subsidies you can argue that the political process has been derailed in favour of special interest groups. If you follow the chain from corn -> HFCS -> diabetes and heart disease, it's not even acting in the citizen's best interests.

Similarly, it's also trade issues that make malaria worse than it has to be. Screens for windows would make it much less likely to spread - but the material is too expensive for most of the people who really need it.