Most of our opinions (on politics at least) are informed by a combination of principle and consequences. In different circumstances, we give different weights to both. A lot of people would argue that if a government allowed torture, the long term consequences would offset any short term gains made by, for example, preventing a terrorist attack. However, even if overall welfare was demonstrably increased over time by a torture policy those same people wouldn't suddenly become torture enthusiasts. That's because torture is wrong no matter what the consequences. When it comes to torture, most people would agree (I think!) that principle trumps consequences.
I feel the same way about free speech. I believe we?re all better off for having it, but even if we weren?t I don?t think anybody has the right to deny us that right.
In other cases, consequences trump principles. I doubt most people care about the principle involved in how the government controls the money supply; they are more likely to be concerned about the effects of any decisions on unemployment or inequality or something.
I think there is a huge temptation to try and merge principles and consequences when intellectual honesty requires that we do our very best to keep them separate.
Say for example Joe has a deeply held conviction that gays should be allowed to adopt children and a study comes out showing a negative impact on children raised by same sex parents. Joe immediately argues that the methodology is flawed and questions the motives of the authors, possibly before he has read the paper. Joe is confusing principle and consequences; there is no formula for weighing one against the other and Joe could still be in the right even if there are negative effects on children.
I read some fancy article explaining that it is impossible to untangle the two concerns. That doesn't mean that we can't try.